34 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



accumulations of tillite and other glacial debris of all kinds are generally 

 readily recognized. That even such extremes have not left indisputable 

 records is apparent to all who are familiar with the controversial literature 

 which has grown up around these phenomena. 



It has been demonstrated beyond dispute that in various periods of 

 the earth's history, from Pre-Cambrian to the Pleistocene, there have been 

 periods of refrigeration and ice accumulation either as local or continental 

 glaciers. It is equally obvious, however, that up to at least the close of the 

 Paleozoic conditions prevailed at times which permitted a uniform distribu- 

 tion of plants and animals over the surface of the earth under uniform condi- 

 tions.^ 



The obvious result of such an apparent conflict of evidence for and 

 against climatic variability in Paleozoic time is to invalidate to some extent 

 the evidence on either hand or to enormously increase our conception of the 

 imperfection of the geological record. The latter alternative would lead 

 us to increase the estimate of past time by an amount sufficient to permit 

 repeated revolutions of enormous extent and at the same time to postulate 

 a total loss of any record of such revolutions. The "geological record," 

 while imperfect, shows no hiatuses of this order in the Paleozoic era. We 

 are permitted to accept with some assurance the general notion that the 

 climate or climates of any period or smaller division of time were influenced 

 by local (at least in time) conditions and dismiss in large measure from 

 consideration, as practical problems of the paleogeography of single units, 

 the broad problems of climatic revolution, except in certain stages where a 

 world change is demonstrable, as at the close of the Paleozoic and in the 

 Pleistocene.^ 



VII. DISTRIBUTION OF THE FAUNA AND FLORA. 



(a) Provincial or Cosmopolitan. 



The fauna or flora of any unit may be peculiar in a greater or lesser 

 degree to that unit, or they may be part of a widely distributed whole. 

 Such isolation or wide distribution may be due to characters inherent in the 

 animals or plants themselves, or to the character of the inorganic environ- 

 ment. 



(b) Distribution Dependent on the Character of the Biota. 



Animals or plants may become widely distributed, due to some peculiar 

 resistance or adaptability in themselves which permits them to achieve 

 success in widely different environments, as the rats and mice, the Canada 



' White, David, and F. H. Knowlton, Evidences of Paleobotany as to Geological Climate, 



Science, vol. 31, p. 760, 1910. 

 ^ Schuchert, Charles, Climates of Geological Time, Carnegie Inst. Wash. Pub. 192, pt. 11, 

 chap. XXI, 1914, with bibliography. 

 Dacqu6, Grundlagen und Methoden der Palaogeographie, chap. X. 

 Clements, E. F., Plant Succession, Carnegie Inst. Wash. Pub. No. 242, chap, xii, 1916. 



