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 Ullah 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 genera 

 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 B 

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

 were deposited, and regarding their excessive thickness, perm 

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

 cupy in space, and the ages of time which they reveal, ana tn 

 sider to how great an extent each layer collected in those 

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

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

 tributaries, and above all when we advert to the true nature o ^ 

 stratum, the treasures which it contains, the secrets which he ° ^ 

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

 deur of the problems connected with the geology of this con 1 ■ ^ 



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



f the straw* 

 actively in progress, with the mapping in of the outcrops 01 



and the description of their organic remains, the field for inv » » 



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



and 



The utmost perhaps 



that 



