Shaler.] 278 [April 20, 



tal accumulations then formed in the neighborhood of Boston. The 

 order of the changes, as developed in this examination, seems to 

 have been, first, the accumulation of an ice sheet, so deep as to move 

 over all tue summits in Southern New England; second, a subsidence 

 of the land to the depth of from one hundred to one hundred and 

 twenty feet below its present position, accompanied, or succeeded, by 

 a rapid melting of the glacial envelope, leaving behind it a confused 

 mass of stones of various sizes, sand and mud commingled together 

 without distinct stratification, this sheet varying in thickness from 

 a few feet on the summits of the hills to one or two hundred feet at 

 the mouths of the valleys of the Charles and the Mystic ; third, 

 an elevation of the land which restored it to almost its present level, 

 possibly to a point a little above the level it now has. 



After the disappearance of the great glacial sheet, the shore remained 

 depressed for a sufficiently long time to allow the tidal currents of the 

 coast to wear away a large part of the unstratified deposit from the 

 ice, reopening the fiords and river valleys which had been to a great 

 extent clogged with this debris. Inasmuch as the actual amount of 

 the work done by these marine currents is progressively greater and 

 greater, as we pass from the uppermost points where its action is vis-, 

 ible, down to the present level of the sea, we may conclude that it is 

 likely that this shore began to rise immediately on the retreat of the 

 glacier, and came slowly towards its present position. 



Hitherto I have seen but few evidences of the existence of true 

 moraines in the New England drift. Most of my study of the phe- 

 nomena was done before I had ever seen glaciers at work, or had ex- 

 amined the evidences of their former action in the valleys of regions 

 where all the drift material is attributable to their work. Without 

 this practical knowledge it is really impossible to interpret the work 

 done during the glacial period. Within the last two years, with the 

 preparation of a year's study of the glacial phenomena of Switzer- 

 land, I have been able to recognize at sundry points some features 

 which looked like true terminal moraines; but these are generally so 

 far modified by the action of subsequent erosion, which has gone on 

 in the valley where they are found, that their true character has not 

 been clearly apparent. A few days ago, however, I found in the val- 

 ley of the Charles, near Watertown, a mass of drift material disposed 

 in the most unmistakable moraine shape. The ridge of the moraine 

 may be traced from a point a few hundred feet from the north bank 

 of the river at the eastern end of the United States Arsenal grounds 



