A College Text-Book of Geology

A College 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. 1909 edition. Excerpt: ...America.1 Lower types. Sponges were present in some abundance throughout the period. It is probable that many of the low, simple forms classed as protozoans existed, but only a few identifiable forms have been found. Implied life. The existence of so much animal life implies much vegetable life to supply the necessary food, as heretofore noted. Furthermore, various characteristics of the fossils suggest the presence of animals not known from fossils. A large percentage of the known Cambrian animals were provided with shells, tests, plates, or other forms of hard coverings. In the main, these appear to have been protective devices, and imply enemies or combative rivals against which protection was needed. Perhaps the Howchin, Quar. Jour. Geol. Soc. Vol. LXIV, p. 237. most significant feature of the protective devices lies in the fact that they are usually of the same type as those possessed by the similar animals of later times. The shells of the gastropods, pelecypods, and brachiopods differ from those of to-day in minor features only. The coverings of the trilobites were much like those of their living relatives, and much the same may be said of nearly every form. If there had been a radical change in the character of their enemies or rivals, we might expect some notable change in the defensive devices. It is a natural inference, therefore, that the conflicts of life in the Cambrian seas were similar to those of the present time. The inference may be pushed a step further, and the deduction drawn that the conflicts which led to the evolution of the defensive devices were much like those throughout the period of their retention. Stage of evolution represented. What stage of advancement in the development of life had been already attained...show more

Product details

  • Paperback | 292 pages
  • 189 x 246 x 15mm | 526g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236899806
  • 9781236899804