BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 4, PP. 299-304, PL. 10 JULY 31, 1893 



SOME MARYLAND GRANITES AND THEIR ORIGIN 



BY CHARLES ROLLTX KEYES 



(Bead before the Society December SO, 1892) 



CONTENTS 



Page 



The Granites 299 



Where found in Maryland 299 



Their niinera Iridic Composition 300 



Four Types represented 300 



Origin of the ( Jranites 300 



Two Theories advanced 300 



Localities favorable for < >bservations 300 



Inclusions and their < !< mtacts 301 



Proofs of their eruptive Nature 302 



a. Their field Relations 302 



b. Their Inclusi< >ns 303 



c. Their contact Phenomena 303 



d. Microscopic Examinations 304: 



The Granites. 



Where found in Man/loud. — The granitic rocks of Maryland have lately 

 received special attention, both microscopically and in the field. They 

 occupy small areas, a dozen or more in number, scattered through the 

 eastern part of the central zone of the state, known as the Piedmont 

 plateau. This belt is essentially a crystalline one, made up almost en- 

 tirely of gneisses, which are broken through in numberless places by 

 gabbros, pyroxenites and granites, and other closely related types of 

 igneous rocks. 



The different areas may be known from the chief places within their 

 respective borders. They are Port Deposit, Texas, Windsor road, Relay, 



XLV-Bcix. GEor,. Soc. Am., Vol. 4, 189U. (290) 



