J. D. Dana on the. Glacial era. 



mine whether tliis phenoniction is oonstiint tliroughout the 

 genus, or whether it does or does not occur among allied 

 genera. 



Art. XXIL— xYofe to Article I, on the Quaternary of the Xew 

 Haven Region ; by J. D. Dana. 



As my statement in regard to tlio cs.<ential indrpciMlciKc ..f 

 the Connecticut valley glacier, and others, in the (ihn i;il .im m.iv 

 be misunderstood, I would draw attcntifjn totlie mc;inni;j ..i iliV 

 words "under the Continental glacier" iji tlie notc^ m jml;.' 2.- 

 in whicU it is implied that such glaciers are l>ut ihr mlmor 

 portions of the great Continental glacier. I hoM ihai, uhilr tin 

 veiy large valleys of the land, like th.w.>..t tin- {\.iiiirciiciii 

 and Hudson, had great influence in (h^icnuiniiiL: the .Inaction 

 of the movement in these valleys, csl)(^•i;lliv ihat :ilwiig thr ;ixi> 

 of each, the whole movement must have he'en more or less modi- 

 fied by the movement of the great northern ice-mjii^s ; and tliat 

 the counteracting influence of a vailev depended not onlv on 

 Its depth and extent, but also on its direction and slope. "The 

 smaller transverse valleys caused no modification of the general 

 glacier movement ; but large transverse valleys gave to the ice in 

 the middle of the channel their own course almost unmodified: 

 if not when the great ice-mass had its maximum thickness, at 

 least afterward w^hen it had become thinner and had lost some 

 of its motioi^ 



I may allude to one other example, as I believe it is, of a 

 partly independent glacier— that of the St Lawrence valley ; 

 for the scratclies on its rocks correspond mainly with its course, 

 the prevailing direction, according to Dr. Dawson, being north- 

 east. It should be said that these scratches are attributed by 

 i)r.^ Dawson to icebergs in the Glacial era, which are supposed 

 ith westward up the valley, the land 

 ^ ^ ' as to allow of 



.__ that direction; and 



that bouldei-s were transported up the valley is given 

 mce in favor of this view. But, as in the case of the 



K. Scr.-THiRD Series, Vol I. No. a-FEB., 1871. 



