HISTORY OF THE EARTH 



307 



of the record itself is now exposed and accessible ; and much of 

 that portion still awaits investigation. It is clear, then, that 

 the story of the earth can be little more than outlined, as yet, 

 and that it grows more obscure as we trace it back into the 



remote past. 



QUESTIONS 



1. What is suggested by the finding of sea shells 

 in a series of horizontal beds on top of a mountain 

 3000 feet high, as in Figure 310? 



2. What changes may be inferred from the sec- 

 tions of sedimentary rocks represented in Figures 311, 312, and 313 ? 



FiG.311. Sandstoneand FIG. 312. Limestone FIG. 313. Conglomer- 

 conglomerate. and shale. ate and sandstone rest- 



ing on folded schist. 



3. As between the fishes and the mammals, which would you 

 expect to find preserved in the older rocks ? Why ? 



4. What would be indicated by finding a comparatively recent 

 group of fossils in beds lying beneath rocks which contained much 

 older types ? 



5. What kinds of fossils would you expect to find in sediments 

 deposited in river valleys, as against those laid down in the open sea ? 



6. In what_k.ind of volcanic rocks might fossils be found ? Why 

 not in the others ? 



REFERENCES ON HISTORICAL GEOLOGY 







CHAMBERLIN and SALISBURY : Geology, Vols. II, III. (New York, 



1906.) 



An excellent and elaborate account of the history of the earth. 

 JORDAN and HEATH : Animal Forms. (New York, 1902.) 



An easily understood description of the more important types 

 of animals as they are to-day. 

 JORDAN and KELLOGG : Evolution and Animal Life. (New York, 



1907.) 

 LUCAS : Animals of the Past. (New York, 1902.) 



An interesting explanation of the preservation of animals as 

 fossils, with a description of certain groups which are now extinct. 

 SCOTT: An Introduction to Geology. 2d ed. (New York, 1907.) 



