Page images
[ocr errors][merged small]


31. Reversed Fault .......

32. Single Thrust-plane

33. Section across Coal-basin of Mons (M. Bertrand)

34. Section from Quinaig to Head of Glenbeg (Geol. Survey)

35. Synclinal Double-fold ......

36. Anticlinal Double-fold

37. Diagram of Mountain Flexures ....

38. Diagram of Anticlinal Mountains ....

39. Synclinal Valley shifting toward Anticlinal Axis

40. Section across the Swiss Alps (A. Heim) .

41. Summit of Santis, East Side (A. Heim) .

42. Section across the Schortenkopf, Bavarian Alps (E. Fraas)

43. Section across the Kaisergebirge, Eastern Alps (E. Fraas)

44. Section across the Val d'Uina (Glimbel) ....

45. Sichelkamm of Wallenstadt (Heim) ....

46. Section across the Northern Limestone Alps (E. Fraas) .

47. Section across the Diablerets (Renevier) ....

48. Section across Dent de Morcles (Renevier)

49. Inversion and Overthrust in the Mountains South of the Lake of

Wallenstadt (E. Fraas, after A. Heim)

50. Symmetrical Flexures of the Jura Mountains .

51. Section across Western part of the Jura Mountains (P. Choffat)

52. Section across part of the Sandstone-zone of the Middle Carpathians


53. Section across part of the Middle Carpathians (Vacek)

54. Section across the Appalachian Ridges of Pennsylvania (H. D

Rogers) .........

55. Unsymmetrical Folds, giving rise to Escarpments and Ridges

56. Structure of the Ardennes (after Cornet and Briart) .

57. Diagrammatic Section across a Plateau of Erosion .

58. Section across portion of Southern Uplands, showing Old Red Sand

stone resting upon Plain of Erosion

59. Section from Glen Lyon to Cam Chois (Geol. Survey)

60. Section of Normal Fault......

61. Normal Fault, with High Ground on Downthrow Side .

62. Normal Fault, with High Ground on Upcast Side .

63. Faults in Queantoweep Valley, Grand Canon District (Dutton)

64. Ranges of the Great Basin (Hinman, after Gilbert: length of section

120 miles)

65. Section from the Mediterranean across the Mountains of Palestine to

the Mountains of Moab (after M. Ulanckenhorn).

66. Section across the Vosges and the Black Forest (after Penck)

[ocr errors]


67. Section of Coal-measures nearCambusnethan, Lanarkshire, on a true

scale 166

G8. Section on a true scale across " Tynedale Fault," Newcastle Coal-field 168

69. Section across Great Fault bounding the Highlands near Birnam,

Perthshire ........... 169

70. Section across Great Fault bounding the Southern Uplands . . 170

71. Diagram Section across Horstgebirge 170

72. Mountain of Granite 175

73. Plain of Granite overlooked by Mountains of Schists, etc. . . 176

74. Diagrammatic Section of a Laccolith showing Dome-shaped Eleva

tion of Surface above the Intrusive Rock (after G. K. Gilbert) . 177

75. View of Necks—Cores of old Volcanoes (Powell) .... 188

76. Section of Highly Denuded Volcano, Miuto Hill, Roxburgshire . 189

77. Diagrammatic Section across the Valley of the Tay, near Dundee . 190 7S. View of Mesa Verde and the Sierra el Late, Colorado (Hayden's Report for 1875) 203

7.). Wind Erosion: Table-Mountains, etc., of the Sahara (Mission de

Chadamcs) ........... 254

80. Wind Erosion: Harder Beds amongst inclined Cretaceous Strata,

Libyan Desert (J. Walther) 254

S1. Wind Erosion : Stages in the Erosion and Reduction of a Tablemountain (J. Walther) 255

82. Manganese Concretions weathered out of Sandstone, Arabah Mount

ains, Sinai Peninsula (J. Walther) 256

83. Formation of Sand-dunes 259

84. Advance of Sand-dunes ......... 259

85. Longitudinal Sections of Lake-basins on a true scale . . . 293

86. Sea-cliff cut in Horizontal Strata 3x9

87. Sea-cliff cut in Strata dipping Inland 320

88. Sea-cliff cut in Strata dipping Seaward 320

89. Sea-cliff cut in Beds dipping Seaward 323


Plate I. Joints in Granite, Glen Kunach, Cairngorm (from a photograph

by W. E. Carnegie Dickson) to face 200

Plate II. Weathering of Joints in Granite, Cairngorm Mountains (from a

photograph by W. E. Carnegie Dickson) . . . to face 202

[ocr errors][ocr errors][merged small]




WHEN geologists began to 1nquire into the origin
of surface-features, they were at first led to
believe that the" more striking and prominent of these
had come into existence under the operation of forces
which had long ago ceased to affect the earth's crust
to any marked-extent. It is not.hard to understand
how this conception arose. The' earlier observers
could not fail 'to be. impressed by the evidence of
former crustal disturbances which almost everywhere
stared them in the face. Here they saw mountains
built up of strangely fractured, contorted, and jum-
bled rock-masses; there, again, they encountered the
relics of vast volcanic eruptions in regions now practi-
cally free from earth-throes of any kind. In one place
ancient land-surfaces were seen intercalated at inter-

vals among great successions of marine strata; in other places, limestones, evidently of oceanic origin, were found entering into the framework of lofty mountains far removed from any sea. It was these and similar striking contrasts between the present and the past which doubtless induced the belief that the earth's crust, after having passed through many revolutions more or less catastrophic in character, had at last become approximately stable—the occasional earthquakes and volcanic disturbances of recent times being looked upon as only the final manifestations of those forces which in earlier ages had been mainly instrumental in producing the varied configuration of the land. Mountains and valleys belonged to earth's Sturm und Drang period. That wild time had passed away, and nc>w-old age, with its lethargy and repose, had supefven.ecL L The tumultuous accumulations of stony .clay,"blocks and boulders, gravel and sand that overspread extensive areas in temperate latitudes were- T/eJieved to be the relics of the last great catastrophe-Which had affected the earth's surface. Some notable, xlisturbance of the crust, it was thought, had cause'd^ihe'waters of northern seas to rush in devastating waves across the land. When these diluvial waters finally retired, then the modern era began—an era characterised by the more equable operation of nature's forces.

But with increased knowledge these views gradually became modified. Eventually, it was recognised that no hard-and-fast line separates past and present.

« PreviousContinue »