AMERICAN GEOLOGY EATONIAN ERA, 1820-1829. 273 



tuck}' forever. Strata began to consolidate, ponds and marshes 

 decreased, animals multiplied, and vegetation overspread the soil. 



The sixth period, that of Peleg's flood, was one of catastrophe. 

 Great volcanic eruptions in Europe and America, with awful earth- 

 quakes convulsed the Atlantic Ocean. During this period the Atlantic 

 land disappeared leaving only the volcanic islands — Azores, Madeira, 

 Canary, and Cape Verde — to mark its position. 



It will be remembered that in 1793 Benjamin De Witt noted the 



great diversity among the bowlders along the shore of Lake Ontario 



and recognized the fact that such must have been conveyed there b} T 



some extraordinary means. The means conceived of 



Dobson's Obser- T . - , ,. , , . 



vation on the b} r De Witt were indeed extraordinary and nothing 



less than a ''mighty convulsion of nature." Peter 

 Dobson, a Connecticut cotton manufacturer, writing thirty-two years 

 later, showed himself a better observer and more gifted in powers of 

 deduction. 



In a letter to Benjamin Silliman, dated November 21, 1825," Dobson 

 described bowlders which were unearthed at Vernon, Connecticut, 

 while excavating preliminary to the erection of a cotton factory, as 

 "worn smooth on their under side as if done by their having been 

 dragged over rocks and gravel ly earth in one stead y position.' 1 They 

 also showed scratches and furrows on the abraded, parts. He could 

 account for these appearances only by calling in the aid of ice along 

 with water, the blocks having been worn by being suspended and 

 carried in ice over rocks and earth under water. 



These observations seem to have attracted no attention at the time, 

 and even Edward Hitchcock, thirteen years later, attached no serious 

 importance to them, although his attention was called to the matter by 

 another letter from Dobson, this time addressed to Hitchcock himself. 

 In this second letter, written in 1838, Dobson described the bowlders as 

 having been first rounded by attrition and then worn flat on one side 

 by a motion that kept them in one relative position, as a plane slides 

 over a board in the act of planing. Some of them he describes as 

 worn and scratched so plainly that there was no difficulty in pointing 

 out which side was foremost in the act of wearing, a projecting bit of 

 quartz or feldspar protecting the softer material behind it. In this 

 letter he again announced his inability to account for these appearances 

 except on the supposition that the boulders had been enveloped in ice 

 and moved forward over the sea bottom by currents of water. The 

 drifting icebergs off the Labrador coast he thought might well 

 illustrate the conditions and methods of their production. 



Perhaps it may have been because Dobson was a cotton manufac- 

 turer and not a member of the learned profession, or there may have 



"This may be found in American Journal of Science, X, 1826. 

 NAT mus 1904 18 



