396 GENERAL BIOLOGY 



As there is a tremendous pressure of the superincumbent layers 

 upon the underlying strata, the lower layers as well as their fossil con- 

 tents are often crushed and injured. Extreme care must, therefore, be 

 taken to interpret one's findings. One can readily grasp what such 

 pressure would accomplish in the delicate layers of shale (called paper- 

 shales) which range from sheets as thin as paper to layers of such sheets 

 fifty feet or more in thickness. 



A study of the fossil remains of plants and animals should show us 

 in what order these organisms lived and followed each other in times 

 long past, and it is usually conceded that they do ; but, it is not an un- 

 common thing to find an earlier fossil layer lying above a later one. 

 Geologists explain this by saying that changes have again taken place 

 which reversed these lower beds, or thrust earlier strata between other 

 layers. All this complicated arrangement lends itself to deceptive inter- 

 pretation. For example, those who oppose the usually accepted geo- 

 logical evidence of "periods of time" and "successive ages" say that the 

 arrangement of the various strata is so deceptive that it can only be 

 explained by a world-upheaval of some kind, and that, therefore, no evi- 

 dence of successive ages is worth anything.* 



An interesting example of the order in which certain strata have 

 been formed, is found in instances where trees and their stumps are 

 found lying in a more or less semi-upright position. Often the stump- 

 part and roots still lie in their position of growth or at least they lie in 

 a deeper stratum than the upper and less heavy portion. Such trees 

 were either pushed over by streams of water or carried along by the 

 stream. The heavier end became caught or weighted, and sank, while 

 the upper end remained in a position of slant in the direction of the 

 current. It is, of course, also possible that the trees were entirely sub- 

 merged while still. growing, but in the latter case the rate of sand-deposit 

 must have been sufficiently rapid to lay down an accumulation of at 

 least forty feet (enough to cover the erect tree) before the wood de- 

 cayed. 



Former regions have been identified by the occurrence of great 

 quantities of drift-wood found in the strata, as having been quite close 

 to land, while differences in climate are evidenced by the finding of 

 tropic plant and animal remains in cold regions, and arctic plants and 

 animals in tropic regions. 



Migrations of plants and animals from one region to another are 

 demonstrated by their fossil remains being found in different types of 

 strata in different ages. 



However, no one can tell the number of years required to lay down 

 the various strata any more than he can tell how many years elapsed to 

 form the intervals between such laying down; and these intervals 



*G. McC. Price, "The Fundamentals of Geology." 



