near Mount Washington. 19 



have preceded the last advance of the North American ice sheet 

 over the White Mountains, for the bowlder clay of the region 

 extends far up the troughs, nearly if not quite to their heads. 

 Signs of alternation of the side slopes of certain troughs by heavy 

 regional glaciation obliquely across them, likewise, point to an 

 early origin of the cirques. Extensive piles of angular blocks 

 of local rock on the floors of the ravines, at their very heads, 

 resemble deposits in the "basins" of Mount Ktaadn in Maine, 

 which Tarr believed to be valley glacier moraines. If that is 

 indeed their nature, Alpine glaciers existed in these cirques after 

 the ice sheet melted away ; but it is important to note that such 

 glaciers were scarcely half a mile in length and filled less than 

 half the length of the troughs which the earlier glaciers had 

 carved. If, on the contrary, these block piles are not moraines 

 but late glacial or post-glacial avalanche debris, as appears to 

 be the case, they indicate that when the ice sheet last melted 

 away from the White Mountains no local glaciers whatever 

 were re-established. As a working hypothesis it is suggested 

 that the local White Mountain glaciers developed during one 

 of the early epochs of glaciation, possibly the Kansan epoch, 

 and that the last, Wisconsin, epoch was attended by wholesale 

 regional glaciation without local snowfields and valley glaciers. 



Dartmouth College, Hanover, N. H. 



Art. II. — An Improved Method of Cleaning Diatoms ; 

 by John M. Blake. 



Diatoms are microscopic organisms near the dividing line 

 between animals and plants. It is important for our purpose 

 that they have siliceous skeletons which take on very many 

 symmetrical and beautiful shapes. The chlorophyl and organic 

 matter with which they are associated can be destroyed by 

 strong acids, but they still retain the clay and sand which was 

 deposited with them. The process of cleaning consists in 

 removing this foreign material. Unless this is done the forms 

 will be obscured and difficult to detect. 



Many observers have studied and classified the numerous 

 species, and have spent much labor in preparing and mounting 

 them for observation, for there is a fascination in these forms 

 that appeals to all, and any plan for facilitating and lessening 

 the labor of preparation would be likely to induce many more 

 to take up the study. 



