88 C. D. Walcoit — The Geologist at Blue 3Iomitain. 



represented by the Cumberland and Shenandoah valleys. As 

 this process continued and the river lowered its channel the 

 Blue ridge began to take shape as a distinct feature in the land- 

 scape. Slowly but surely the softer beds were broken up, dis- 

 solved and carried away, and the harder beds of rock began to 

 project above the ancient plateau. It was only the question of 

 which beds of rock could the longer resist the forces of rain and 

 frost to determine the location of mountains and valleys. 



We have thus hastily sketched the evolution of a portion of 

 the continent and the evolution of one of its topographic fea- 

 tures as shown by the Blue ridge. This evolution has gone on 

 everywhere. Every ridge, however small ; every valley, whether 

 shallow or deep, narroAV or broad ; every stream-channel all 

 over the surface of the continent, has its history back in the 

 past, and it is by the studies of the geologists that we learn 

 something of that history. It is now nearly forty years since 

 William B. and H. D. Rogers discovered many elements of the 

 structure of the Appalachian mountains ; but it was not until 

 within the last few years that the means of correlating and thus 

 interpreting more accurately the structure of the various mount- 

 ains formed by the lower and oldest series of the sedimentary 

 rocks have been obtained. 



During the deposition of the 40,000 feet of sediments in the 

 Appalachian trough many millions of invertebrate animals lived 

 and died along the shore and on the sea-bed. Those that lived 

 iu the earlier epochs became extinct and new forms succeeded 

 them, and these in turn were succeeded many times during the 

 vast interval between the first deposit and the closing one before 

 the epoch of the last Appalachian uplift and folding. The re- 

 mains of the various groups of life now afford the data by which 

 the geologist correlates the various disturbed and often separated 

 masses and determines Avhat were their original relations to each 

 other. 



There are hundreds of local details yet to be studied and in- 

 terpreted, and the work will be done by those who love to study 

 the record of creation in the fragmentary book of nature, where 

 all is written that we know of the past before barbaric man 

 began his imperfect record by myth and legend. 



