RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 301 



ful production of human reasoning and the best possible general stand 

 ard which can be adopted before a comparatively full investigation of 

 the geology of the whole earth has been made, it is not, and cannot 

 be except in a general way, of universal applicability. That is, while 

 the respective stages and substages of the scale are recognizable only 

 by means of their characteristic fossil remains, it has been shown that 

 any of those characteristic forms are so liable To range from one stage 

 or substage to another that it is impossible to sharply define the limits 

 of stages, and often impossible to distinguish substages in one part of 

 the world as they are known in another part. 



The facts and principles which are enunciated and explained in this 

 essay are of great importance in discussions of the relative chronologi- 

 cal value of the different kinds of fossil remains and of the correlation 

 of series of strata in separate regions of the earth, both of which sub- 

 jects will, however, be specially discussed in following essays. 



There is another subject which, if more data were available, might 

 be profitably discussed at length in this connection. This subject re- 

 lates to what may be designated as paleoclimatic conditions,* that is, 

 to formerly existing conditions, which in certain parts of the earth were 

 more or less materially different from those which now exist in the 

 same parts. The evidence that such climatic changes have occurred 

 upon the earth's surface consists of the presence of the fossil remains 

 of kinds of animals and plants the living congeners of which could not 

 exist in such a climate as now prevails there. For example, abundant 

 fossil remains of arboreal floras are found in Greenland far north of the 

 present northern limit of trees, and fossil corals are found at various 

 localities in similar latitudes which are still farther beyond the northern 

 limit of living coral- forming polyps. 



These and similar cases must be taken as positive proof that great 

 changes of climate have occurred upon the earth, but there are other 

 cases which are frequently accepted as evidence of such changes that 

 are of a more doubtful character. That is, +here is much reason to 

 believe that certain kinds of animals and plants formerly lived under 

 climatic conditions which their nearest living congeners seem incapable 

 of enduring. For example, the natural range of living elephants, 

 rhinoceroses, and palms does not reach beyond a warm-temperature 

 climate, but remains of certain species of those animals have been found 

 where arctic winters prevail, and they are known to have been pro 

 vided with a hairy protection against the cold. Remains of palms 

 have also been found associated with those of fossil floras that indicate 

 at least a cool temperate, if not a more severe, climate. 



There is a multitude of other facts which bear upon this subject, but 

 only these references to it are introduced here to indicate it as one of 

 those which the geologist needs to bear in mind in all his biological 

 investigations, especially those which pertain to correlation. 



* Il^Xaio^, ancient; KAijita, climate. 



