78 Transactions of tee A^ierican Institute. 



of natural science upon the American continent. The suljject upon 

 wliich I design to speak to vou is the geological history of the Isorth 

 American Continent. 



Geologists do not consider the American continent as the product 

 of sudden action. Geology, in fact, in its progress, has s]lo^vn us, 

 step by step, that long periods in the past have existed while the 

 changes on the surface of the globe have been going on very 

 much as they are now going on ; periods of time so vast and 

 so extended in the past that the geologist who has studied most 

 earnestly for a lifetime comprehends more fully than any one else the 

 sublimity of that passage, " In the beginning God created the heavens 

 and the earth;" for that "beginning" has to us the significance of 

 being incomprehensible in the past as eternity in the future. Before 

 speaking, however, of the subject at hand, I beg leave to call your 

 attention to some of the processes going on upon the surface of the 

 earth at the present time. This will make more intelligible to you 

 what I shall say in regard to the manner of the distribution of 

 materials over the ocean bed. 



Upon every portion of the surface of the earth we have mountain 

 chains, plains, and valleys ; and we have rocks, loose materials, sand, 

 pebbles, gravel, and other substances of that kind, wliich are distri- 

 buted over the surface. These are distributed, not uniformly, but 

 according to certain laws, which have prevailed in all geologic time. 

 This pebble, for example, which I have before me, has at one time 

 been an angular fragment of stone, broken from a rock which had 

 itself been, at a still earlier time, a loose mass of sand, which has 

 been consolidated. It has become rock. It has again been broken, 

 and these pebbles have been triturated by the action of the water, the 

 action of the sea, or of rivers and streams, until the angles have been 

 worn oft', and the surface rounded ; the finer materials being gradually 

 worn away and disappearing in the deeper water, reduced by its 

 action to an impalpable condition. The harder particles of material 

 like this make the sand which strews the sea beaclies everywhere. 

 The sand was not derived from tlie breaking down of sandstone, but 

 from the breaking down of materials containing sand or silex. While 

 the finer and less palpal^le, and the more soluble portions have been 

 widely separated, tlie harder portions, which are a silicious sand, 

 remain to make sea beaches and river beaches. In this respect nature 

 is constantly active. There has been no moment of time when this 

 process, this degradation of tlie surfiiee of the globe was not going 



