THE GLACIAL HYPOTHESIS 305 



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 were described 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 the appearances 

 except on the supposition that they had been enveloped in ice and 

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

 icebergs of the Labrador coast he thought might well illustrate the 

 conditions of their production. 



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

 turer and not a member of one of the learned professions, or there 

 may have been other reasons, but Hitchcock allowed the observations 

 to pass unnoticed until 1842, when the subject was brought up by 

 Sir Eoderick Murchison in his anniversary address before the Geolog- 

 ical Society of London. 



I take leave of the glacial theory in congratulating American science in 

 having possessed the original author of the best glacial theory, though his name 

 has escaped notice, and in recommending to you the terse argument of Peter 

 Dobson, a previous acquaintance with which might have saved volumes of dis- 

 putation on both sides of the Atlantic. 



Supported by this somewhat enthusisastic endorsement, Hitchcock 

 then gave the letter to the public through the American Journal of 

 Science, at the same time remarking that he had himself derived his 

 ideas concerning the joint action of ice and water from the writings 

 of Sir James Hall. 



With this much in the way of anticipation, I will turn back to 

 1825 once more and refer to the writings of William Keating, mineralo- 

 gist, who accompanied Major Long's expedition to the sources of the 

 St. Peters Eiver. This observer noted that the entire region of the 

 present headwaters of the Winnipeek Eiver had been at a comparatively 

 recent period an immense lake, interspersed with innumerable barren 

 rock islands, which had been drained by the bursting of the barriers 

 which tided back the waters. This was plainly a recognition of the 

 now extinct glacial Lake Agassiz. 



Although the cosmogonist was fast drifting into the obscurity of 

 the past, there were, nevertheless, occasional writers who preferred tc 

 ignore facts of observation or the efficiency of simple causes, and to 

 seek for more difficult or more mystical methods of accounting for 

 phenomena than those afforded by the observation of processes now in 

 action. Thus, Benjamin Tappan, in discussing in 1828 the boulders 

 of primitive and transition rocks found in Ohio, objected to the com- 

 monly accepted idea that such were necessarily foreign to the locality 

 and brought by currents of water or floating ice. He frankly acknowl- 



voi,. r,xvin. — 20. 



