276 Prof. Rogers's Address before the 



the vast amplitude of several miles, and chase each other with an enor- 

 mous velocity, equal in many instances to twenty or thirty miles per 

 minute. This movement we are disposed to impute to an actual pulsa- 

 tion in the fluid lava mass, upon which the thin crust of the earth is sup- 

 posed to rest, excited by a sudden rupturing and instantaneous collaps- 

 ing of the crust, rent by the tension of highly elastic steam and other 

 vapors. 



In a previous year we drew the attention of the Association to the 

 remarkable structural features of the Appalachian chain, and showed 

 that these laws of earthquake action furnish perhaps the only solution 

 of the origin of those grand flexures and folds into which the Appa- 

 lachian strata have been bent, so extraordinary for their regularity, 

 great length, parallelism, wave-like form, and progressive subsidence 

 westward ; and in illustration of the power of earthquakes thus to pro- 

 duce permanent anticlinals, we instanced among other cases the eleva- 

 tion in 1819 of UUah Bund, a low, broad mound, fifty miles in length, 

 lifted from the flat plain of the delta of the Indus by the great earth- 

 quake of Cutch. 



Having now passed in review some of the more important general 

 conclusions in relation to our geology to which recent researches have 

 led, we may turn for a moment before closing to contemplate the mag- 

 nitude and enticing interest of the field for future discovery, which these 

 explorations have made accessible. 



When we reflect on the enormous expansion of some of our great 

 systems of strata, nothing short of the entire ancient seas in which they 

 were deposited, and regarding their excessive thickness, permit our 

 thoughts to dilate until they can take in the true areas which they oc- 

 cupy in space, and the ages of time which they reveal, and then con- 

 sider to how great an extent each layer collected in those ancient 

 seas is now exposed to view, on the flanks of our huge mountain chains 

 and in the banks and cliffs of our mighty rivers and their unnumbered 

 tributaries, and above all when we advert to the true nature of each 

 stratum, the treasures which it contains, the secrets which lie locked 

 within it, — we become aware of the inexhaustible variety and the gran- 

 deur of the problems connected with the geology of this continent. 



Let us not think that with the completion of the explorations now so 

 actively in progress, with the mapping in of the outcrops of the strata, 

 and the description of their organic remains, the field for investigation 

 will have become exhausted. It will in fact only have become opened 

 up for more minute and critical research. The utmost perhaps that 



