Abstract ........................................................ 1
Introduction .................................................... 1
Historical Background ........................................... 1
Geologic Setting ................................................ 2
Physiography ................................................. 2
Bedrock Geology .............................................. 4
Cenozoic Landscape and Surficial Deposits .................... 7
Introduction .............................................. 7
River Morphology .......................................... 9
Alluvial Terraces ........................................ 10
Abandoned Entrenched Meanders ............................ 10
Recent Flood-Plain Alluvium .............................. 11
Colluvium ................................................ 14
Karst Landforms .......................................... 14
Fossils Along the C&O Canal ................................. 14
Introduction ............................................. 14
Piedmont Province ........................................ 15
Blue Ridge Province ...................................... 16
Valley and Ridge Province ................................ 17
Cambrian Fossils ...................................... 17
Ordovician Fossils .................................... 17
Silurian Fossils ...................................... 22
Devonian and Mississippian Fossils .................... 22
Engineering Geology ......................................... 22
Introduction ............................................. 22
Canal Excavation and Towpath ............................. 23
Locks and Lock Stone ..................................... 23
Cement ................................................... 25
Aqueducts, Culverts, and Waste Weirs ..................... 30
Dams ..................................................... 31
Control of Geology on Engineering ........................... 31
Geologic Guide ................................................. 32
Piedmont Province—Potomac Terrane ........................... 34
Georgetown Section of Washington, D.C., to Seneca, Md.
(MM 0 to MM 23) .......................................... 34
Access Points ......................................... 34
Introduction .......................................... 34
Georgetown to Glen Echo Park Area (MM 0 to MM 7) ...... 36
Glen Echo Park Area to Swains Lock (MM 7 to
MM 16.6) .............................................. 36
Swains Lock to Seneca (MM 16.6 to MM 22.8) ............ 40
Piedmont Province—Culpeper Basin, Westminster Terrane, and
Frederick Valley ............................................ 45
Seneca, Md., to Point of Rocks, Md. (MM 22.8 to
MM 48.2) ................................................. 45
Access Points ......................................... 45
Introduction .......................................... 45
Seneca to Edwards Ferry (MM 22.8 to MM 30.8) .......... 47
Edwards Ferry to Monocacy Aqueduct (MM 30.8 to
MM 42.2) .............................................. 48
Monocacy Aqueduct to Point of Rocks (MM 42.2 to MM
48.2) ................................................. 48
Blue Ridge Province ......................................... 53
Point of Rocks, Md., to Fort Duncan (MM 48.2 to MM 63) ... 53
Access Points ......................................... 53
Introduction .......................................... 53
Point of Rocks to Brunswick (MM 48.2 to MM 55) ........ 55
Brunswick to Fort Duncan (MM 55 to MM 62.5) ........... 55
Valley and Ridge Province—Great Valley Section .............. 65
Fort Duncan to McCoys Ferry (MM 62.5 to MM 110) .......... 65
Access Points ......................................... 65
Introduction .......................................... 65
Fort Duncan to Antietam Creek (MM 62.5 to MM 69) ...... 65
Antietam Creek to Big Slackwater (MM 69 to MM 85.5) ... 68
Big Slackwater to Williamsport (MM 85.5 to MM 99.5) ... 70
Williamsport to McCoys Ferry (MM 99.5 to MM 110) ...... 72
Valley and Ridge Province—West of North Mountain Thrust
Fault ....................................................... 76
McCoys Ferry to Cumberland, Md. (MM 110to MM 184.5) ...... 76
Access Points ......................................... 76
Introduction .......................................... 76
McCoys Ferry to Licking Creek Aqueduct (MM 110 to MM
116) .................................................. 78
Licking Creek Aqueduct to Round Top Cement Mill (MM
116 to MM 127.5) ...................................... 78
Round Top Cement Mill to Sideling Hill Aqueduct (MM
127.5 to about MM 137) ................................ 80
Sideling Hill Aqueduct to Paw Paw Tunnel (MM 137 to
MM 156) ............................................... 88
Paw Paw Tunnel to Oldtown (MM 156 to MM 167) .......... 90
Oldtown to Spring Gap (MM 167 to MM 173.5) ............ 91
Spring Gap to Cumberland (MM 173.5 to MM 184.5) ....... 91
Acknowledgments ................................................ 93
References Cited ............................................... 93
Appendix 1— Sources of Data—Geologic Maps of 7.5-Minute
Quadrangles .................................................... 99
Plates
1 Geology of the Chesapeake and Ohio Canal National
Historical Park and Potomac River Corridor, District of
Columbia, Maryland, West Virginia, and Virginia
[in pocket]
2-20 Geologic maps of the Chesapeake and Ohio Canal
National Historical Park and Potomac River Corridor
from: 2 Georgetown (MM 0) to near Glen Echo Park
(about MM 7) ............................................ 107
3 Near Glen Echo Park (about MM 7) to Swains Lock
(MM 17) .............................................. 109
4 Swains Lock (MM 17) to Seneca (MM 22.8) .............. 111
5 Seneca (MM 22.8) to Edwards Ferry (MM 30) ............ 113
6 Edwards Ferry (MM 30) to Monocacy River Aqueduct
(MM 42.2) ............................................ 115
7 Monocacy River Aqueduct (MM 42.2) to Point of Rocks
(MM 48.2) ............................................ 117
8 Point of Rocks (MM 48.2) to Brunswick (MM 55) ........ 119
9 Brunswick (MM 55) to Fort Duncan (MM 62.5) ........... 121
10 Fort Duncan (MM 62.5) to Antietam Creek (MM 69) ...... 123
11 Antietam Creek (MM 69) to Big Slackwater (MM 85.5) ... 125
12 Big Slackwater (MM 85.5) to Williamsport (MM 99.5) ... 127
13 Williamsport (MM 99.5) to McCoys Ferry (MM 110) ...... 129
14 McCoys Ferry (MM 110) to Licking Creek Aqueduct
(MM 116) ............................................. 131
15 Licking Creek Aqueduct (MM 116) to Round Top Cement
Company mill (MM 127.5) .............................. 133
16 Round Top Cement Company mill (MM 127.5) to Little
Orleans (MM 141) ..................................... 135
17 Little Orleans (MM 141) to Paw Paw Tunnel (MM 156) ... 137
18 Paw Paw Tunnel(MM 156)to 0ldtown (MM 167) ............ 139
19 Oldtown (MM 167) to Spring Gap (MM 173.5) ............ 141
20 Spring Gap (MM 173.5) to Cumberland (MM 184.5) ....... 143
Figures
1 Sketch map showing the geologic provinces in the
mid-Atlantic region and the locations of the Chesapeake
and Ohio (C&O) Canal, the Potomac River, and the Potomac
River basin ................................................. 2
2 Maps showing the earliest beginnings of canal transport ..... 3
3 Tectonic map of the study area .............................. 5
4 Diagrammatic sketches showing the geologic history of
the Potomac River valley over the past 1 billion years ...... 6
5 Maps of alluvium and alluvial terraces of the Potomac
River ....................................................... 8
6 Schematic cross sections of the Potomac River valley at
Cumberland, Md. (A-A'), and the Georgetown section of
Washington, D.C. (B-B') ..................................... 9
7 Sketch map showing large water-filled potholes and
channels on the eastern half of Bear Island near MM 13 and
Widewater .................................................. 10
8 Potholes in migmatite of the Neoproterozoic and (or)
Lower Cambrian Mather Gorge Formation along the bluff of
Mather Gorge in Virginia ................................... 11
9 Aerial photograph showing fish weirs constructed by
Native Americans ........................................... 11
10 Remnants of Quaternary alluvial terraces ................... 12
11 Sketch maps illustrating the evolution of the abandoned
incised meanders of the Potomac and Little Cacapon Rivers
near Paw Paw, W. Va ........................................ 12
12 Schematic maps of the Great Falls of the Potomac River
showing the evolution of the abandoned channel of
Widewater and of Glade Hill ................................ 13
13 Rounded boulder of diabase (5 ft in diameter) deposited
by the Potomac River on terrace at south end of Glade
Hill ....................................................... 13
14 Recent alluvium along the Monocacy River ................... 13
15 Schematic map showing the distribution of carbonate rocks
and noncarbonate rocks along the C&O Canal and Potomac
River corridor ............................................. 14
16 The cave at Dam 4 near MM 83.5 ............................. 15
17 Fossils from rocks of the Frederick Valley section,
western Piedmont province .................................. 16
18 Dinosaur tracks in the Upper Triassic Balls Bluff
Siltstone exposed in the Culpeper Stone Co. quarry near
Culpeper, Va ............................................... 17
19 Brachiopods in Silurian and Devonian rocks ................. 17
20 Key index fossils present in the rocks found along the
C&O Canal in the Valley and Ridge province ................. 18
21 Key guide conodonts to the strata of the Valley and Ridge
province ................................................... 20
22 Map showing locks, aqueducts, dams, and known quarries
near the canal ............................................. 24
23 Stone berms constructed to prevent erosion between the
towpath and the Potomac River .............................. 25
24 An example of modern erosion in the canal near Lock 34
(west of MM 62) ............................................ 25
25 Evidence of excavated bedrock .............................. 26
26 Historical photographs of Paw Paw Tunnel, near MM 155 ...... 26
27 Examples of Lower Cretaceous Potomac Formation ............. 27
28 Upper Triassic Poolesville Member of the Manassas
Sandstone .................................................. 27
29 East end of Lock 24 (Riley's Lock at MM 23) ................ 28
30 Nonfoliated Ordovician Ellicott City Granodiorite .......... 28
31 Quartzite of the Lower Cambrian Weverton Formation ......... 28
32 Limestone of the Lower Cambrian Bolivar Heights Member
of the Tomstown Formation .................................. 29
33 Lock 60 at MM 149.5 ........................................ 29
34 Round Top Cement Company, west of Hancock, Md .............. 29
35 Seneca Creek Aqueduct, just east of MM 23 .................. 30
36 The Monocacy River Aqueduct at MM 42 ....................... 30
37 Historical photograph (1936) of Dam 3 ...................... 31
38 Dam 6, which was located north of Great Cacapon, W. Va.,
near MM 134 ................................................ 32
39 Historical photograph (1940) showing reconstruction of
the towpath and canal at Widewater ......................... 33
40 Excavation of the canal through bedrock .................... 33
41 Generalized structure map and cross section of a portion
of the C&O Canal National Historical Park and Potomac
River corridor as it crosses the Piedmont province and
easternmost part of the Blue Ridge province ................ 35
42 Part of a National Historical Marker where the C&O Canal
enters Rock Creek .......................................... 36
43 Igneous rocks of the Early to Middle Ordovician
Georgetown Intrusive Suite near Key Bridge in Washington,
D.C ........................................................ 37
44 Sandstone cobbles along canal .............................. 38
45 Undeformed sedimentary melange of the Lower Cambrian
Sykesville Formation at MM 9.8 ............................. 38
46 Sheared melange of the Lower Cambrian Sykesville
Formation near MM 11.5 ..................................... 38
47 The Great Falls of the Potomac River ....................... 39
48 Phyllonite of the Neoproterozoic and (or) Lower Cambrian
Mather Gorge Formation near MM 12.5 ........................ 39
49 Migmatite of the Neoproterozoic and (or) Lower Cambrian
Mather Gorge Formation ..................................... 40
50 Migmatite of the Neoproterozoic and (or) Lower Cambrian
Mather Gorge Formation ..................................... 41
51 Dark amphibolite within the Neoproterozoic and (or) Lower
Cambrian Mather Gorge Formation intruded by white
pegmatite of the Ordovician(?) Bear Island Granodiorite .... 42
52 Milky white, fractured vein quartz intruding
metagraywacke of the Neoproterozoic and Lower Cambrian
Mather Gorge Formation near Widewater near MM 13.5 ......... 42
53 Underground gold mine north of Great Falls Tavern .......... 43
54 Late Devonian lamprophyre dikes intruding metagraywacke
of the Neoproterozoic and (or) Lower Cambrian Mather
Gorge Formation ............................................ 44
55 Folding in metagraywacke and schist of the Neoproterozoic
and (or) Lower Cambrian Mather Gorge Formation ............. 44
56 Folded metagraywacke of the Neoproterozoic and (or) Lower
Cambrian Mather Gorge Formation ............................ 45
57 Sheared phyllite and folded white vein quartz of the
Neoproterozoic(?) and Lower Cambrian(?) Ijamsville
Phyllite that lies above the Martic thrust fault along
the Monocacy River ......................................... 47
58 Tightly folded, thin-bedded limestone within the
Ijamsville Phyllite along the Monocacy River ............... 47
59 Metasiltstone of the Lower and Middle Cambrian Araby
Formation showing foliation with near-vertical cleavage
along the CSXT railroad north of MM 43 ..................... 48
60 Examples of the varieties of limestone in the Upper
Cambrian Frederick Formation ............................... 49
61 Conical hill north of Nolands Ferry and Maryland Route 28
representing topographic inversion ......................... 49
62 Stereoscopic pair of aerial photographs showing the
change in the morphology of the Potomac River valley in
the Piedmont province across the boundary between the
Culpeper basin and Potomac terrane ......................... 50
63 Conglomerate of the Upper Triassic Reston Member of the
Manassas Sandstone that forms the base of the Culpeper
basin ...................................................... 50
64 Limestone conglomerate interbedded with red siltstone of
the Upper Triassic Leesburg Member of the Balls Bluff
Siltstone .................................................. 51
65 Limestone conglomerate of the Upper Triassic Leesburg
Member of the Bull Run Formation ........................... 51
66 Lower Cambrian Tomstown Formation .......................... 52
67 Lower Cambrian rocks of the Blue Ridge province ............ 52
68 Generalized structure map and cross section of a portion
of the C&O Canal National Historical Park and Potomac
River corridor as it crosses the westernmost part of the
Piedmont province, the Blue Ridge province, and the
easternmost part of the Great Valley Section ............... 54
69 Neoproterozoic Catoctin Formation .......................... 55
70 Stereoscopic pair of aerial photographs and sketch
centered on Point of Rocks, Md ............................. 56
71 Pods of marble in the Neoproterozoic Swift Run Formation ... 56
72 Basement rocks of the Blue Ridge province .................. 56
73 Weverton Cliffs at the southern end of South Mountain in
Maryland ................................................... 57
74 Polymictic conglomerate of the Lower Cambrian Loudoun
Formation north of the Potomac River on the east flank
of South Mountain .......................................... 58
75 Mesoproterozoic rocks between Weverton, Md., and Harpers
Ferry, W. Va ............................................... 58
76 Stereoscopic pair of aerial photographs and sketch
centered on Harpers Ferry, W. Va., showing the Potomac
River gorge and water gap .................................. 59
77 Sketch of the bluffs of Elk Ridge north of the C&O Canal ... 60
78 View of eastern end of Elk Ridge ........................... 60
79 Historical photograph of the westernmost overturned
anticline of quartzite in the Lower Cambrian Buzzard Knob
Member of the Weverton Formation ........................... 61
81 View of the westernmost overturned anticline shown in
figure 80 .................................................. 61
80 Historical photograph showing the easternmost overturned
anticline in quartzite of the Lower Cambrian Buzzard Knob
Member of the Weverton Formation ........................... 61
82 Crossbedding in quartzite of the Lower Cambrian Weverton
Formation at Maryland Heights .............................. 62
83 Geologic sketch of the bluffs from about MM 61 to the
Great Valley west of Lock 36 (MM 62.5) ..................... 62
84 Folded and cleaved metasiltstone of the Lower Cambrian
Harpers Formation .......................................... 63
85 Cleavage in metasiltstone of the Lower Cambrian Harpers
Formation folded as the result of motion along a thrust
fault ...................................................... 64
86 Outcrops of Lower Cambrian Harpers and Antietam
Formations ................................................. 64
87 Generalized structure map and cross section of a portion
of the C&O Canal National Historical Park and Potomac
River corridor as it crosses the western part of the Blue
Ridge province and the Great Valley section of the Valley
and Ridge province ......................................... 66
88 Geologic sketch from about MM 65.2 westward ................ 67
89 Limestone of the Lower Cambrian Bolivar Heights Member of
the Tomstown Formation near MM 68 .......................... 67
90 Examples of karst features in the Fort Duncan Member of
the Tomstown Formation near MM 68 .......................... 68
91 Outcrops of Lower and Middle Cambrian Waynesboro
Formation in the vicinity of the C&O Canal ................. 69
92 Historical photograph (around 1895) showing Botelers and
Reynolds Cement Mill's quarries in near-vertical
limestone (in West Virginia opposite MM 71.6) and
Botelers and Reynolds Dam for mill race for the cement
mill ....................................................... 69
93 Historical sketch (around 1867) of soldiers and citizens
in and around Killiansburg cave near MM 75.7 ............... 70
94 Historical photograph (date unknown) showing location
north of Dam 4 ............................................. 70
95 Geologic sketch from McMahons Mill near MM 88 westward
to Lock 41 depicting Ordovician rocks of the older
Stoufferstown Member of the Stonehenge Limestone thrust
above limestone of the younger Rockdale Run Formation ...... 71
96 Mylonitic limestone within the Lower Ordovician
Stoufferstown Member of the Stonehenge Limestone ........... 71
97 Depositional features in the Lower and Middle Ordovician
Rockdale Run Formation ..................................... 72
98 Historical photograph (around 1920) of Cushwa basin
at Williamsport (MM 100) ................................... 73
99 Upper part of Middle Ordovician Martinsburg Formation
along the railroad north of MM 101 ......................... 73
100 Geologic sketches showing structures in Cambrian and
Ordovician rocks of the Great Valley section of the
Valley and Ridge province .................................. 74
101 Mudcracks on Upper Cambrian and Lower Ordovician
Conococheague Limestone at MM 107.8 ........................ 75
102 Stromatolites in the Middle and Upper Cambrian Elbrook
Limestone east of McCoys Ferry ............................. 75
103 Upper Ordovician and Lower Silurian Tuscarora Quartzite .... 76
104 Side-looking airborne radar (SLAR) image, generalized
structure map, and cross section of a portion of the C&O
Canal National Historical Park and Potomac River
corridor as it crosses the Valley and Ridge province,
including the westernmost part ............................. 77
105 Fort Frederick and Big Pool at MM 112 ...................... 79
106 Historical photograph of workers and mules scraping the
floor of Big Pool after it was drained to remove silt ...... 79
107 Upper Silurian and Lower Devonian Helderberg Limestone
and Lower Devonian Shriver Chert ........................... 80
108 Thin-bedded sandstone and shale of the Upper Devonian
Brallier Shale ............................................. 80
109 Upper Devonian Foreknobs Formation ......................... 81
110 Middle Devonian Marcellus Shale southeast of MM 125 in
West Virginia .............................................. 82
111 Historical photograph of the Devil's Eyebrow ............... 82
112 Sketch of the Devil's Eyebrow and ruins of Round Top
Cement Company mill west of Hancock, Md .................... 83
113 Folds in Upper Silurian Bloomsburg and Wills Creek
Formations ................................................. 83
114 Historical photograph (1897) looking down the axis of an
anticline .................................................. 83
115 Shale of the Middle Silurian Rose Hill Formation ........... 84
116 Historical photograph from the overlook on Cacapon
Mountain in West Virginia .................................. 84
117 Geologic sketch of the bedrock along the section of the
C&O Canal from east of MM 133 west to Dam 6 and Tonoloway
Ridge ...................................................... 85
118 Middle Silurian Keefer Sandstone ........................... 85
119 Geologic sketch of folded and faulted rocks of the Upper
Silurian Wills Creek Formation east of MM 134 .............. 86
120 Folded and faulted strata at Fluted Rocks .................. 86
121 Upper Silurian and Lower Devonian Helderberg Limestone ..... 87
122 Brachiopods in Lower Devonian Oriskany Sandstone
underlying Tonoloway Ridge at Dam 6 ........................ 87
123 Outcrop of Lower and Middle Devonian Needmore Shale ........ 87
124 Historical photograph (undated) showing folded and
faulted shale and sandstone of the Upper Devonian
Brallier Shale ............................................. 87
125 Mississippian rocks of the Sideling Hill syncline .......... 88
126 Sandstone in the Upper Devonian and Lower Mississippian
Rockwell Formation exposed along the Sideling Hill Creek
Aqueduct at MM 136.5 ....................................... 88
127 Structures in the Upper Devonian Brallier Shale ............ 89
128 Upper Devonian Brallier Shale near MM 155 .................. 90
129 Reckley Flat, north of MM 160 .............................. 91
130 Devonian Hampshire Formation, exposed east of Town Creek
on the limb of the Town Creek syncline ..................... 91
131 Lower Devonian Oriskany Sandstone on the west limb of
the Broadtop anticline ..................................... 91
132 Upper Devonian Brallier Shale near MM 172 .................. 92
133 Historical photograph showing the C&O Canal and wharf
area at Cumberland ......................................... 92
Table
1 Dimension stone used for the C&O Canal locks and
aqueducts and the source geologic unit ..................... 25
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