SAYLES: THE SQUANTUM TILLITE. 159 



one hand that the slate masses are pebbles and on the other that they 

 are pockets of slaty material laid down during the deposition of the 

 conglomerate." 



The slate masses referred to above are very similar to the slate 

 lumps in the beds under the tillite at Atlantic. I consider their 

 origin to be similar; disruption by moving ice and transportation by a 

 glacial stream would explain it. No undoubted tillite has appeared 

 north of Sciuantum Head and Roslindale, but clay fragments could 

 have been transported by glacial streams beyond the ice-front for 

 some distance. It is difficult to understand how clay particles could 

 have been deposited in isolated pockets in so swift a stream as is 

 indicated in this exposure by the size of the pebbles and boulders. 

 Some of the boulders measure ovf r a foot in diameter. 



Cleavage is found at this exposure. It does not appear that this 

 rock is tillite. 



Locality 15. Waban. About half way between Eliot and Wa- 

 ban railroad stations there is an outcrop on the south side of the 

 track. The strike is N 38° E, and the dip o3°X., as determined from 

 overlying slate. This rock is not tillite but has every appearance of 

 being on the tillite horizon. It is a very coarse conglomerate. The 

 largest boulders are at least two feet in diameter, and are of angular, 

 subangular, and rounded shapes. Melaphyre tuff appears to under- 

 lie this conglomerate. Above the conglomerate are beds of sandstone 

 transitional to a thick body of slate, which appears to be the Cam- 

 bridge slate. This very coarse conglomerate may well be outwash 

 material from the glacier. It is several miles west of the most westerly 

 outcrop of tillite. 



Locality 16. Moon Island. At the most eastern extremity of 

 Moon Island, which is, as a matter of fact, artificially connected with 

 Squantum by a viaduct, there is an outcrop of the tillite. The 

 strike is N 70° E, and the dip about vertical. The matrix is very fine 

 suggesting the lower part of a tillite bed. There is no stratification 

 and the included rock fragments are mostly angular, and subangular. 

 No striated pebbles have been searched for. Some intercalated beds 

 of sandstone and conglomerate may be seen. As this place was found 

 very recently it does not appear on the locality map, and the criteria 

 for tillite are not yet as complete as possible. Moon Island is a drum- 

 lin, and at the tillite outcrop well-exposed till lies on the tillite. 



Criteria found: — A, B, C, D, J, K, L. 



Locality 17. Huifs Cove. At Huit's Cove, Hingham, on the east 

 shore of Weymouth Back River, there is an exposure of the very top 



