82 PROCEEDINGS OF THE r-HILADELPHIA MEETING 



femic magma, and (b) that a striking uniformity exists tlirougtiout the series 

 ill rangs and subrangs. 



The uniformity denotes consanguinity ; the distribution, through all the 

 classes (class 1 to class 5), magmatic differentiation. No alkaline differenti- 

 ates are found ; neither feldspathoid nor soda-bearing pyroxenes are original 

 ( onstituents of any type. The differentiated magmas are almost without ex- 

 ception alkalicalcic. docalcic or percalcic, and presodic. 



In areal distribution the acidic types are most abundant and the gabbroid 

 types second in abundance ; the most acidic and the most basic differentiates 

 are least widely distributed. 



The possible origin of a peculiar granodiorite through marginal assimilation 

 by the gabbro of the acidic gneiss into which it intrudes was discussed, and 

 some features of the anorthosite occurrence were presented. 



Presented by title in the absence of the author. 



MAGMATIC ASSIMILATION 

 BY F. BASCOM 



(Ahstract) 



Near Strathcona, Vancouver Island, Canada, lime and magnesian silicates 

 (epidote, chlorite, serpentine) have been developed in a diorite batholith to a 

 distance of 1,400 feet from an included lens of limestone (40 to 50 feet wide) : 

 750 feet south of the lens small irregular masses of limestone are included in 

 the altered diorite, while three-fourths of a mile to the south the diorite is 

 of a normal character. The rocks have been named the Sutton limestone and 

 AYark diorite by C. H. Clapp (Memoir No. 1.3, Can. Geol. Survey). 



Read by title, drawings being on view in exhibition room. 



HYPERSTHENE SYENITE (AKERITE) OE THE MIDDLE AND NORTHERN BLUE 



RIDGE REGION, VIRGINIA 



BY THOMAS L. WATSON AND JUSTUS H. CLINE 



(Abstract) 



Several seasons of field work by the Virginia Geological Survey in the middle 

 and northern parts of the Blue Ridge and adjacent portions of the Piedmont 

 plateau in Virginia have shown the dominant igneous rock of- the granitoid 

 type to be a quartz-bearing pyroxene syenite, the important facies of which is 

 similar in composition to the akerites of Norway described by Brogger. This 

 igneous mass, of which pyroxene syenite is the chief type, probably represents 

 a pre-Cambi"ian batholithic intrusion exposed more or less continuously for a 

 distance of 150 miles in a belt up to 20 miles or more in width. 



Differentiation of the syenite mass has given rise to a variety of related 

 rocks, some of which are of unusual types. Microscopic study of many thin 

 sections shows the important minerals of the syenite in descending order of 

 abundance to be soda-lime feldspar (albite to andesine-Iabradorite, chiefly 



