IGNEOUS ROCKS 319 



cases they are distinct^ connected with the great gabbro intrusive, and 

 presumably there is connection when it is not evident. 



Such dikes occur H miles south of I than on Ithan creek, one-half mile 

 north of Ithan, one-half mile southeast of Villa Nova, in the Schuylkill 

 section near Spring Mill, one-half mile north of Bryn Mawr station, on 

 Crum creek in Willistown township, parallel to Crum creek in the neigh- 

 borhood of Swarthmore, on Chester creek near Ridgewater, on Rocky run 

 in Middletown township, at Edgemont and west of Edgemont in Edge- 

 mont township, at Valley Falls station on the Penny pack creek, near 

 Vereeville on the same creek, at Ogontz, and at other localities. 



Character. — An analysis by W. F. Hillebrand of a dike of meta-gabbro 

 occurring 1 mile north of the Bryn Mawr station is as follows : 



Analysis of meta-gabbro dike, Roberts road, Bryn Mawr 



Si0 2 48.68 Zr0 2 Not estimated. 



A1 2 3 14.39 P 2 5 0.29 



Fe 2 3 4.00 01 Not estimated. 



FeO 10.09 T Not estimated. 



MgO 6.32 s Trace. 



CaO 9.23 Cr A None. 



Na 2 2.31 Ni0 • • • • Trace - 



K 2 0.47 Mn0 ■•■ °- 22 



jj q j_ 2 03 ^ a ^ Faint trace. 



H 2 — 0.46 Sr0 None - 



C0 2 None. Li *° Trace_? 



Ti0 2 1.69 100.18 



Norm 



Quartz 2.82 Magnetite 5.80 



Orthoclase 2.78 Ilmenite 3.19 



Albite 19.39 Apatite 0.67 



Anorthite 27.52 H 2 2.49 



Diopside 13.67 



Hypersthene 21.78 100.11 



The rock falls into class III, order 5, rang 4, subrang 3— that is, it is a 

 hornblende-grano-auvergnose. 



Like the gabbro mass to which it is probably genetically related, it is 

 perfelic, docalcic, and presodic, though it is slightly more basic, the 

 femic constituents being. equal to the salic. 



HORNBLENDE-GNEISS 



In addition to the basic dikes above described there occurs a larger 

 body of hornblende-gneiss whose areal distribution is concealed by a 

 covering of younger materials. Quarries on the outskirts of Frankford ; 



