162 bulletin: museum of comparative zoology. 



On Blue Hill Avenue opposite Hazelton Street, just north of Walk- 

 hill Street, there is an outcrop of slate and an unstratifiecl conglomeratic 

 mass resembling tillite. Other doubtful deposits are as follows: — 



On railroad between Wollaston and Quincy. 



Black's Creek, one fourth mile west of railroad. 



North Quincy, one half mile northeast of Atlantic station. 



Between Florence St. and Hyde Park Avenue, near Mt. Hope 

 station. 



Cleavage. 



As noted in the description given of the tillite, evidence of intense 

 shearing is found in every locality. The cleavage dips, as a rule, 

 in a northeasterly direction. The shearing is beautifully shown in 

 some of the pebbles from the tillite, which have been split in two and 

 the parts turned as if on a pivot. In a boulderet found at Squan- 

 tum Head one half has been sheared from the other about one third 

 of an inch at one end, while at the other end only slight displace- 

 ment has been effected. Some of the pebbles have been indented, 

 and others flattened and stretched. A great many have a puck- 

 ered or wrinlded appearance suggesting flow-effects. Striations due 

 to diastrophic movements may be found frequently and are en- 

 tirely different from the glacial striae. Almost all the surfaces of 

 the rock fragments in the tillite have been thus affected in some 

 manner. ^Yith all the shearing, and other diastrophic mo\ements 

 which the pebbles in the tillite have been through it is not to be won- 

 dered at that glacially striated pebbles and boulders are rarely found. 

 Occasionally one of the surfaces of a pebble has been so placed in the 

 matrix of the tillite as to escape the violent diastrophic movements. 



Some of the tillite exposures have been weathered and it is nearly 

 useless to look for striae in these. At Hyde Park where Dr. La Forge 

 found the best striated pebble yet brought to light, the rock has been 

 freshly blasted and there is more hope of a successful search. There 

 is also an advantage here in a search for striations, in that the bottom 

 of the tillite is exposed. As mentioned above, till contains finer 

 materials and more striated pebbles at the bottom than at the top 

 (Stone, 1899, p. 29-30). ^Yherever the bottom of the tillite has been 

 found the matrix is much finer than in the places where the top is 

 exposed. The difficulties experienced in extricating pebbles from 

 the fresh matrix of the bottom of the tillite has been very great. 

 Most of those taken out have been broken in many fragments. All 

 of the striated pebbles but one were found near the bottom of the 



