1884 19 [Crosby. 



ion, can be seen in contact with it on the north side, the surface 

 of contact being a fault plane trending nearly east-west and 

 inclined to the north about 75°. That parallel with this fault 

 the conglomerate, which, from the predominance of the pinite 

 debris, is largely of a soft and slaty character, exhibits a well- 

 marked cleavage structure, the pinite pebbles being flattened and 

 the rigid felsite pebbles broken in a way to indicate a powerful 

 compression in a direction normal to the fault-plane. And, fin- 

 ally, that the strike of the conglomerate is northeast and south- 

 west, the dip very steep to the southeast, and that this is clearly- 

 shown in a ledge on Central Avenue a few rods southwest of the 

 felsite ledge. Here a coarse conglomerate or breccia alternates 

 with layers of sandstone, so that the stratification is very plain. 



Every important proposition which I have affirmed in this 

 statement is denied by Dr. Wadsworth. He says that the felsite 

 is merely a portion of the conglomerate altered by thermal 

 waters ; that the strike of the conglomerate is east-west, the bed- 

 ding being parallel with the fault-plane and the supposed cleav- 

 age, which he says is not cleavage, but merely stratification. He 

 says, further, that the large, angular fragments in the breccia are 

 slate resembling the slate on the railroad one-third of a mile 

 northeast of this locality ; thus proving that the conglomerate is 

 younger than the slate. 



First, with regard to the felsite. The contact between it and 

 the conglomerate is well defined. On one side of a perfectly 

 definite plane is the soft and distinct slaty conglomerate and on 

 the other side is the purple felsite of almost flinty hardness, and 

 showing no pebbles. This felsite is similar to and almost contin- 

 uous with that covering a large area in this part of Milton west 

 of Central Avenue and south of the Neponset River. In the 

 neighboring ledges there are two varieties, white and purple. 

 These occur separately, irregularly mixed, and very regularly and 

 beautifully banded or interlaminated. Traces of this ban ding are 

 observable in the ledge of felsite on Central Avenue. Dr. Wads- 

 worth says this felsite contains many argillaceous pebbles but 

 partly obliterated. These supposed pebbles are in part the irreg- 

 ular and broken banded structure and in part are due to the 

 crushing of the rock along the fault. All geologists know that 

 what are called crush breccias are of common occurrence in the 



