Shaler.] 196 [January 19, 



January i9, 1870. 



Vice President Dr. C. T. Jackson in the chair. Forty three 

 persons present. 



The following paper was read : — 



On the Parallel Ridges of Glacial Drift in Eastern 

 Massachusetts, with some Remarks on the Glacial Pe- 

 riod. By N. S. Shaler, Professor of Palaeontology, H. U. 



In the immediate neighborhood of Boston the unstratified drift 

 does not lie in anything like a continuous sheet, but is distributed in 

 long and rather narrow ridges, which, with varying height, on ac- 

 count of long continued denudation, may be traced for miles across 

 the country. These ridges are particularly conspicuous in the islands 

 of the harbor of Boston, where, although much worn by the action 

 of the tidal currents, the parallelism is quite apparent. The fact of 

 the existence of this symmetry in the arrangement of these islands 

 was first remarked by Count Pourtales, assistant in the Coast Survey 

 corps. He perceived, what may be readily observed in the accurate 

 map of that survey, that there are two sets of trends exhibited in the 

 arrangement of these islands, the principal being from northwest to 

 southeast, and the other and somewhat subordinate set of ranges run- 

 ning from northeast to southwest, or directly at right angles to the 

 other set. Although the intersecting water level makes these ridges 

 somewhat more conspicuous in the harbor than upon the land, they 

 are, in fact, better marked upon the main land than among the islands. 

 All the high land of Chelsea and Winthrop is composed of half a 

 dozen or more tolerably lofty drift ridges, which retain a remarka- 

 ble parallelism though varying a good deal in altitude, and somewhat 

 in transverse extent. The spaces between these ridges are not quite 

 cut down to the sea level at all points, though at no point much 

 elevated above it. The effect of marine denudation at a time when 

 this shore region was more depressed than it is now, is evident 

 throughout this group of drift hills. The greater part of East Boston 

 seems to be a ridge corresponding in course with those in Chelsea. 

 The general trend of these ridges is northwest and southeast, with 

 few degrees of variation in some cases, but on the whole with as much 

 regularity as is ordinarily observable in any such geographical features. 

 Passing to the westward we find in Charlestown, Somerville, Cam- 



