SAYLES: THE SQUANTUM TILLITE. 169 



logical and what would be expected if the ice came from the southeast. 

 Another indication of the direction of ice movement is found in the 

 limited westward extension of the tillite. To the west beyond Roslin- 

 dale no true tillite has yet been found. Southwest of ^Slt. Benedict 

 in the woods there is a layer of very large boulders in the conglomerate. 

 One of them measures over three feet in diameter and most of them 

 are over two feet. There is a suggestion here of outwash materials 

 and swift water. At Waban in what appears to be the tillite horizon 

 there are more large boulders, but no tillite. To the north of Stiuan- 

 tum Head and Roslindale no undoubted tillite has been found. All 

 of these considerations point to an easterly or southeasterly place of 

 origin. The fact that no terminal moraine has been found is no proof 

 that there was none. The width of a frontal moraine belt varies from 

 a few feet to twenty miles for a continental glacier. A wide belt 

 would probably appear somewhere in these highly folded strata of the 

 Boston Basin, Init a narrow belt might easily have been folded under 

 or already eroded and thus lost to sight. Outw^ash materials, how^ever, 

 would extend for miles beyond the terminal moraine, and that some 

 of the coarse gravels west of Roslindale are of such origin appears 

 possible. 



It is impossible to say whether the glacier w^hich formed the tillite 

 was of the continental or piedmont type. The large thickness of the 

 tillite might indicate either, for thick till is not limited to continental 

 glaciers, but is found in the low lands of the Alps at the present day. 

 The thickest till is almost always found in the valleys (J. Geikie, 1895, 

 p. 24). The boulders and fragments of limestone found by Crosby 

 at Huit's Cove, Hingham, in the tillite, seem to be real exotics, and 

 this might indicate that the ice came from some distance. It is 

 necessary to suspend judgment on this question of type of the glacier. 

 The Malaspina glacier is about se\enty miles long and twenty-five 

 miles wide. A glacier of this size would answer all the requirements 

 of the discoveries in the Boston Basin. The extent of the tillite 

 precludes anything smaller than a piedmont glacier. 



In the vicinity of Squantum and Atlantic the tillite is seen to be 

 made up of three separate beds divided by the two intercalated beds 

 mentioned above. If the intercalated beds near the top are con- 

 sidered, the tillite is divided still farther. Whether the two main 

 intercalated beds indicate interglacial epochs is a question of impor- 

 tance. That such beds indicate milder conditions there can be no 

 doubt, but that such milder conditions would mean an interglacial 

 epoch of long duration is more difficult to prove. All that can be said, 



