6Gi TRANSACTIONS OF THE AMERICAN INSTITUTE. 



tated in the form of granite, gneiss, and many other rocks, there- 

 fore erroneously supposed to be igneous. Many changes took 

 place which the beautiful science of geology studies and tries to 

 explain. Rocks once formed by deposit from water were elevated 

 to enormous heights; brooks and rivers originated; mountains were 

 airain crumbled down, washing earth and pulverulent matters in 

 the lowest places, and formed deposits, partially filling up some 

 depressions. Some of those basins filled up with deposits of car- 

 bonate of lime, full of remnants of ocean shells, were again ele- 

 vated and formed on lime rocks, of which the enormous Catskill 

 ^Mountains in our State are but a small illustration, elevating the 

 aqueous deposits to some 4,000 or 5,000 feet above the surface of 

 the ocean. 



Another force causing this upheaving of mountains must not be 

 overlooked, namely the volcanic action; I need not repeat to you 

 the accounts of uiountains elevated, lavas ejected in enormous 

 quantities in different localities, which of course you have all read 

 about, and Avill only remark that the volcanic action Ave see now, 

 is only an insignificant remnant of what it was once; it appears to 

 have been exceedingly active in the moon, as the inspection with 

 the telescope reveals a greater number of extinguished volcanoes 

 than are on our earth; however we must take in account that here 

 on earth the water has Avashed aAvay and submerged many \-olcanic 

 testimonials, a cause not acting in the moon, Avhich is entirely dry. 



The chief cause that this volcanic action has almost ceased, is 

 that the crust of the earth is much thickei- than some philosophers 

 have lately supposed. You are probably aware that the heat 

 increases one degree Fahrenheit for every thirty or forty feet Ave 

 descend in the earth, and this law holds for so far as we have been 

 able to verify it, that is for the insignificant amount of about 2,000 

 feet deep; it has been concluded from this fact, that when this 

 increase goes on at the same ratio, at the depth of a few miles, 

 every thing is in a melted condition, and as the earth has a diame- 

 ter of 8,000 miles, that we live on a comparatively thin crust; but 

 where is the guarantee that this increase in temperature goes on 

 after the same hxAv? Laplace presented his hypothesis Avith diffi- 

 dence, stating that it is imprudent to go bej'oud direct observa- 

 tion or calculation; but calcuhition comes here to settle the mat- 

 ter, and Hopkins, in P^ngLind, has calculated from the precision 

 of the equinoxes, that the crust can not possibly be thinner than 

 800 to 1,000 miles. This calculation docs not hoAvever exclude 



