WARREN. — ALKALI-GRANITES AND PORPHYRIES. 231 



being quite granitic in appearance; nor did Dr. White's microscopic 

 studies inform Professor Crosby as to the true nature of these rocks. 



Distribution. — The exceedingly detailed and careful study of the 

 relations of this rock to the coarse-granite and to the slates made by 

 Professor Crosby has proved beyond doubt that it is throughout a 

 contact phase of the granite magma. In the Quincy-Weymouth 

 area (see general map, no. 1), viz. that part of the field lying roughly 

 east of the line of the West Quincy Branch of the Railroad as far north 

 as the West Quincy Station, in the area lying north and northwest of 

 the Station in what has been termed the "Furnace Brook" area and 

 also along the northern edge of the alkaline-rocks wherever the fine- 

 granite is exposed as far west, at least, as Canton Avenue in Milton, 

 this rock appears to be the only contact phase of the magma which 

 was developed and this will be termed for convenience the Ruggles 

 Creek type, since the most satisfactory exposures are found in the 

 region about Ruggles Creek and from here the type specimens were 

 chosen for analysis. The other exposures of the fine-granite, viz. 

 in the Pine Hill area. Pine Tree Brook Reservation and in the area 

 lying between Wampatuck and Fox Hill, all of wliich are compara- 

 tively small in contrast to the development of the rock in the Quincy- 

 W^eymouth area of the field, are closely associated with the other 

 contact phases of the magma. The field exposures in these areas, 

 particularly the first two, indicate that in places the fine-granite, often 

 quite porphyritic, replaces the granite-porphyry etc. as the contact 

 phase of the magma against the slate just as it does in the S. Quincy- 

 Weymouth area and along the northern edge of the complex : at other 

 points its relations are more obscure but suggest that there may be fine- 

 granite zone intermediate between the rhombenporphyry and granite- 

 porphyry and the granite. This is perhaps supported by the fact 

 that in such occurrences the rock shows a much stronger porphyritic 

 habit. Actual transitions to the porphyry and coarse granite have 

 not, however, been observed with certainty although numerous sharp 

 contacts have, and it is invaded by dikes of coarser granite just as 

 the porphyry is. No certain contacts can be found for the mass lying 

 between Wampatuck and Fox Hills but there is a strong indication 

 that the fine-granite becomes more porphyritic in the neighborhood 

 of the granite-porpliyry and there may be a rapid transition into it. 



Although actual contacts of the fine-granite with the slate in the 

 Quincy-Weymouth area are apt to be concealed, enough are satis- 

 factorily exposed to show that the rock is somewhat finer in grain at 

 the immediate contact. Against those slate masses which represent 



