40 THE PHYSICAL FEATURES OE CECIL COUNTY 



in three colors, and are divided into Gneiss, Mica Slate, Hornblende 

 Slate, Trap and Serpentine; thns representing the most complex series 

 of rocks which had up to that time been distinguished. 



Professor Williams in 1887 commenced a reconnaissance of the 

 crystalline rocks outside the Baltimore region which he had already 

 studied in great detail. During this season he traced the lines of the 

 geological formations, particularly of the gabbro, northeastward 

 across Harford county to the Susquehanna river and made some- 

 what detailed sections along the Cecil county shore of the river. At 

 the same time he traced the limits of the gabbro body of the region 

 between Conowingo and the Octoraro eastward across part of Cecil 

 county. The results of this preliminary survey were not published in 

 detail but were mentioned in a report on the progress of the work on 

 the Archaean geology of Maryland published the following year. The 

 results of this trip served as a basis for a plan by which the crystalline 

 rocks of Cecil and Harford counties were to be studied in detail by 

 Professor Williams and his students. It was not, however, until 

 1893 that detailed mapping was commenced in Cecil county. In this 

 year Messrs. George P. Grimsley and Arthur G. Leonard commenced 

 field studies of the granites and more basic rocks of the county. Mr. 

 Grimsley published a report on the granites of Cecil county in 1894, 

 in which he emphasizes the conclusions, that the granitic rocks are 

 eruptive masses which have been modified by dynamic action and are 

 probably older than the more basic rocks which bound them on the 

 north and south ; that the granitic rocks are divided into two portions 

 by a belt of staurolitic mica-schist; the rocks near Port Deposit being 

 more gneissoid and foliated and hence representing either an older in- 

 trusion or a zone of maximum dynamic action, while the changes in 

 the northern divisions are mainly chemical resulting in a change of 

 the feldspar to epidote; and that the staurolitic mica-schist separating 

 the two areas of granite represents a sedimentary deposit more ancient 

 than the granites, which probably owes its highly crystalline character 

 to contact metamorphism. 



The work upon the basic rocks commenced at the same time by 

 Mr. Leonard was not completed until some years later and the results 



