544 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



The ort'dir due for this piece of excellent original work is certainl}^ 

 not impaii'ed bv the fact announced by Prof W. M. Davis, in his historical 

 rc'sumt^ of the literature of the subject/ that the same forms had been 

 observed, mapped, and correctly explained by Mr. ]\I. 11. Close," in Ireland, 

 at an earlier date. As, moreover, the name "lenticular hills," proposed h\ 

 Messrs. Hitchcock and Upham, is certainly not a very satisfactory one, and 

 seemed, indeed, not wholly satisfactory to its authors, it is a matter of con- 

 gratulation that the earlier paj^er proposes a name from the Irish, which, 

 with the Scotch, is so nmch richer in names for the varieties of surface 

 form of the land than is our own dialect. Indeed, if the word could come 

 into general use it would be a valuable addition to our synonyms for hill 

 forms, while its more precise use follows a custom already set in this 

 department of study. 



The comparison of drumlins with the sand banks formed beneath 

 flowing water seems quite satisfactory. I have also been interested to 

 compare them with roches moiitonnees, with which they are associated in 

 origin beneath the ice. 



Fig. 31, p. 540, is a representation of a vertical bank of clay and till 

 resting against red sandstone. A broad roche moutonne'e of the red sand- 

 stone, beautifullv striated, was exposed, and abutting against the southern 

 vertical and unstriated wall of the rock was a till of almost equal com- 

 pactness with the rock itself, bounded above by a citrved surface, which 

 was the exact continuation of that of the sandstone. The curve sank 

 under the water above and below. This may Avith some propriety be 

 called half roche moutonn^e and half drumlin, and illustrates the close 

 similarity of the cause originating the two rock forms — the differential 

 pressure of the ice upon its substratum. In several other cases rock takes 

 part in the formation of the drumlin, at times as a nucleus with steeper 

 slo})es than those of the drumlin itself, but appearing along its crest; yet 

 this is the exception here as elsewhere. 



The distribution of these hills along the valley, as shown in PI. 

 XXXV, is interesting, and may thi'ow some light upon the question of the 

 north-south motion of the ice in the valley as compared with the northwest- 

 southeast motion on the higher ground on either side. 



1 Am. Jour. Sci., 3d series, Vol. XXVIII, 1884, p. 407. 

 -Jour. Royal Geol. Soc, Ireland, 1886, p. 1207. 



