118 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
CLASSIFICATION. 
FIELD RELATIONS AND TERMINOLOGY. 
The rocks found within the above-defined area may be grouped 
as follows: — 
1. Sedimentary rocks: — 
Cambrian slates and limestone. 
Newer slates. 
Conglomerate. 
2. Granitoid 1 -(Plutonic) rocks with hypidiomorphic granular 
texture, resulting from subterranean cooling: — 
Diorite and dioritic granite : Extreme basic type. 
Biotite granite (Granitite) ) __ . 
T T -ji -i . V -Normal types. 
Hornblende granite ) J1 
Hornblende granitite: Zonal acidic type. 
3. Porphyritic and Felsitic (Effusiye) rocks, with textures 
which resulted from surface cooling, or from the devitrification of 
glassy rocks. 
A. Acidic. 
Aporhyolite: (Quartz porphyry, felsite) : Extreme acidic type. 
Texture: — 
Porphyritic. 
Fluidally banded. 
Brecciated. 
B. Basic: —- 
Melaphyr. 
4. Dikes of diabase, gabbro, etc., cutting each of the above. 
5. Granite Dikes. 
The above classification seems to represent in a general way the 
succession in age of formation of the rocks involved. However, in 
the case of the igneous rocks, as will be brought out later, there is 
in the Blue Hills a complete series of gradations from the typical 
hornblendic Quincy granite to the most jaspery fluidal aporhyolite. 
Throughout the present paper an effort has been made to simplify 
the use of terms in accordance with recent English usage, rather 
than to adopt the age distinctions employed by German petro- 
graphers. For this reason the name aporhyolite (cipo , altered, and 
rhyolite, from the Greek “to flow”) has been used in general in 
i The classification of rocks here employed is modified from that of Adams (’91), Sears 
(’94), liascom (’93, ’90), Harker (’95), and Kemp (’96). 
