AMERICAN GEOLOGISTS AND NATURALISTS. 27 



north ; those on the east of the Hudson from the northwest, 

 those on the west from the northeast, as by the result of two 

 forces. 



The diluvial furrows are, in general, parallel to the valleys in 

 which they are found : thus in the small transverse valleys, the 

 scratches are found pai-allel to the direction of the valleys, and 

 not coincident with those of the main valleys. All the bowl- 

 ders seem to have been brought from the northwest, both at the 

 east and beyond the river St. Peter's at the west, and very few 

 are found below 38^ or 39° of north latitude. 



The chairman (Prof. Silliman) cited the recorded observa- 

 tions of Mr. C. Darwin, naturalist to H. M. ship Beagle, that in 

 South America no bowlders occur nearer the equator than about 

 40° south latitude. 



Prof. Mather had not seen any bowlders in the coal region of 

 Ohio, and very few in Kentucky. He thought that the bowl- 

 ders mentioned by Mr. Hodge in the gold region of North Caro- 

 lina, were not transported masses, but were composed of granite 

 which had suffered decomposition in situ by atmospheric agency. 



Prof. Henry D. Rogers said there was need of much caution 

 in the use of the term bowlder, as regards the size of the mass to 

 which it should be restricted ; he was inclined to give the term 

 much latitude. Thus he conceived that a current of drift com- 

 ing from the north and meeting the terraces of Pennsylvania, 

 would there be arrested and deposit its larger masses — and so 

 from stage to stage, until the onward current would carry for- 

 ward only the smallest sand ; in this way, we may find among 

 the drift of the south, all the materials derived from the northern 

 rocks. 



He concluded that all the materials of a cmTcnt of drift, find 

 their resting place in accordance with gravity. 



Prof. Mather doubted whether the large bowlders found on 

 Long Island, resting on beds of sand or fine gravel, could be 

 thus accounted for, because a current of sufficient force to move 

 such large masses would have carried away the sand. 



Prof. Rogers replied, that diluvial action could not be restrict- 

 ed to a single epoch. 



We must find in secular and periodical elevation, the cause 

 of the translation of the beds of infusorial earth recently found in 

 the tertiary of Virginia, which are there covered by the quiet 

 strata of the Miocene. We have evidence of numerous slight 

 elevatory movements on the eastern coast of North America, and 



