EVIDENCES— GEOLOGY 



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swallowed grass between the clenched teeth all point to the violence 

 and suddenness of its passing. Almost all of the animal was pre- 

 served, though the hair of the back has disappeared and the trunk 

 had been eaten off by dogs before the specimen was discovered " 

 (Lull). P'ossils of this type, and any others buried in substances 

 with preservative qualities, are, of course, not unlike preserved 

 specimens. The most numerous are the aml)er fossils of the 

 Oligocene (Fig. 68). The ambers are formed by the transforma- 

 tion of resinous exudates from coniferous trees, and in their initial 

 state were of such consistency that even the most delicate insects 



A B C 



Fig. 68. — Amber fossils. A, an ant; B, a mayfly; C, a flea. (From Zittel.) 



could be caught and embedded by them with little damage. As the 

 resins hardened and turned to amber the contained organisms 

 were preserved as in a modern microscopic mount. Thousands of 

 specimens of Arthropoda, chiefly insects, have been discovered in 

 the Baltic amber deposits of Germany, along the coast of the Baltic 

 Sea. Although even such delicate bodies as those of insects have 

 also been fossilized in shales, the amber fossils and frozen and pre- 

 served remains of animals are naturally more complete and perfect 

 than any other kind. 



Fossils preserved in rocks are often broken and distorted by 

 the subsequent movements of the strata in which they lie. Con- 

 sequently they are more often incomplete or imperfect, and de- 

 mand more careful study and interpretation. 



Interpretation of fossils. Environment. The value of fossils 

 is not alone the record of past life which they give us, but also 

 evidence of climatic conditions. In living organisms we can see 

 that certain structures are correlated with certain qualities of 



