Gra?iites of Cecil County, in Xorth-eastern Maryland. 59 



THE GRANITES OF CECIL COUNTY, IN NORTH- 

 EASTERN MARYLAND.- 



By G. Perry Grimsley. 



r. 



FIELD RELATIONS OF THE ROCKS. 



It is proposed, in the following paper, to present the 

 results of a study of the granites of Cecil County, in North- 

 ern Maryland. As the area occupied by these rocks is of too 

 great extent to be thoroughly investigated in the limited time 

 at my disposal, a certain portion of it was chosen which 

 should be representative of the whole region. The area thus 

 selected is roughly triangular in shape, as may be seen from 

 the accompanying geological map. It is bounded on the 

 north by the broad gabbro belt w T hich crosses the river from 

 Harford County ; its south-western boundary is the Susque- 

 hanna River, while the eastern limit is marked by a line 

 drawn south from the town of Rising Sun, across the granite, 

 to the Columbian gravels. No previous geological work has 

 been published on the crystalline rocks of this district, and 

 the accompanying map is the first one to represent, in detail, 

 the geological features of the region. The general effect of 

 the topography is that of a plateau of two hundred feet ele- 

 vation, cut into deeply at the west by the Susquehanna River, 

 and incised to nearly equal depth by the numerous smaller 

 streams. Its surface is gently undulating, except along the 

 river, where the deep channels give the plateau a rugged 

 appearance. The river soon reaches base level, and the towns 

 along its side are only a few feet above the sea. 



The rocks of this region are noncrystalline, with a north- 

 east strike, and a highly-inclined dip to the south-east. The 



:: This paper was accepted by the Johns Hopkins University as a thesis for the 

 degree of Doctor of Philosophy ; and the writer is indebted to Dr. G. H. Williams 

 for kind advice and valuable suggestions during the course of its preparation. 



