FIGURE 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 PAGE 95 95 96 97 97 98 99 42. Section across the Schortenkopf, Bavarian Alps (E. Fraas) Section across the Kaisergebirge, Eastern Alps (E. Fraas) Section across the Val d'Uina (Gümbel) III 112 112 Section across the Northern Limestone Alps (E. Fraas) 113 47. Section across the Diablerets (Renevier) 113 48. Section across Dent de Morcles (Renevier) 114 Wallenstadt (E. Fraas, after A. Heim) 49. Inversion and Overthrust in the Mountains South of the Lake of 50. Symmetrical Flexures of the Jura Mountains 51. Section across Western part of the Jura Mountains (P. Choffat) 116 53. Section across part of the Middle Carpathians (Vacek) Section across part of the Sandstone-zone of the Middle Carpathians 116 117 54. Section across the Appalachian Ridges of Pennsylvania (H. D. Rogers) 55. Unsymmetrical Folds, giving rise to Escarpments and Ridges 58. Section across portion of Southern Uplands, showing Old Red Sandstone resting upon Plain of Erosion 59. Section from Glen Lyon to Carn Chois (Geol. Survey) 60. Section of Normal Fault. 146 153 61. 62. Normal Fault, with High Ground on Downthrow Side 155 156 63. Faults in Queantoweep Valley, Grand Cañon District (Dutton) 65. Section from the Mediterranean across the Mountains of Palestine to FIGURE 67. Section of Coal-measures near Cambusnethan, Lanarkshire, on a true scale. 68. Section on a true scale across "Tynedale Fault," Newcastle Coal-field 69. Section across Great Fault bounding the Highlands near Birnam, Perthshire. 70. Section across Great Fault bounding the Southern Uplands 71. Diagram Section across Horstgebirge 72. 73. Mountain of Granite Plain of Granite overlooked by Mountains of Schists, etc. 74. Diagrammatic Section of a Laccolith showing Dome-shaped Elevation of Surface above the Intrusive Rock (after G. K. Gilbert) View of Necks-Cores of old Volcanoes (Powell) 75. 76. Section of Highly Denuded Volcano, Minto Hill, Roxburgshire PAGE 166 168 169 170 170 176 177 188 189 190 79. Wind Erosion: Table-Mountains, etc., of the Sahara (Mission de 254 80. Wind Erosion: Harder Beds amongst inclined Cretaceous Strata, 254 81. Wind Erosion: Stages in the Erosion and Reduction of a Table- 82. Manganese Concretions weathered out of Sandstone, Arabah Mountains, Sinai Peninsula (J. Walther). 85. Longitudinal Sections of Lake-basins on a true scale 86. Sea-cliff cut in Horizontal Strata 87. Sea-cliff cut in Strata dipping Inland 259 259 Plate I. Joints in Granite, Glen Eunach, Cairngorm (from a photograph to face 200 to face 202 EARTH SCULPTURE CHAPTER I INTRODUCTORY EARLY VIEWS AS TO ORIGIN OF SURFACE-FEATURES-ROCKS AND ROCK-STRUCTURES-ARCHITECTURE OF THE EARTH'S CRUST -GENERAL EVIDENCE OF ROCK-REMOVAL. WHEN geologists began to inquire 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 jumbled rock-masses; there, again, they encountered the relics of vast volcanic eruptions in regions now practically 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 now old age, with its lethargy and repose, had supervened. The tumultuous accumulations of stony clay, blocks and boulders, gravel and sand that overspread extensive areas in temperate latitudes were believed to be the relics of the last great catastrophe which had affected the earth's sur face. Some notable disturbance of the crust, it was thought, had caused the 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. |