A Text-Book of Geology

A Text-Book of Geology

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 edition. Excerpt: ...hedding and columnar structure, near Catskill, N. Y. 208. Ripple and rill marks.--The former may be observed on almost any shallow bottoms where the waters are stirred by the wind. They may be covered by quiet later deposition and preserved. Perfect examples are thus found in the most ancient sedimentary formations. When the waves retire from a shelving sand beach, little rills of water flow down the incline and erode small channels in the sand. They may excavate pockets about an opposing pebble or shell. Such structures are likewise found on the surface of layers of ancient sandstones. Fig. 96.--Hippie marks on Triassic sandstone. Turner's Falls, Mass. Slab 43 b-24 inches, of which one half is here shown. Photograph by N. V. State Museun.. 209. Rain prints and sun cracks.--Let the water soak away from a roadside pool, and raindrops splash upon the soft surface mud. A roundish impression is made which may even show the direction in which the rain fell. Or the drying of the mud shrinks and cracks it into rough polygonal blocks. Let another rain ensue, and the fresh supply of mud will fill the cracks and cover the bottom of the pool anew, thus making a cast or mold of the cracked layer. Both this structure and the rain prints are sometimes found in splitting open beds of ancient rocks. 210. Fossils.--These are commonly small structures, sometimes harder, but often softer, than the rock which holds them. In the latter case especially they are a source of weakness, and favor the disintegration of the mass. While not very important as physical structures save in Fig. 98.--Sandstone, showing ancient mud cracks. Portland, Conn. Photograph by W. H. C. Pynchon. their contribution to the limestones of the world, they are of supreme importance in...
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Product details

  • Paperback | 104 pages
  • 189 x 246 x 6mm | 200g
  • United States
  • English
  • black & white illustrations
  • 1236506804
  • 9781236506801