84 THE CRYSTALLINE ROCKS OF CECIL COUNTY 



The material collected by these geologists and by Dr. Edward B. 

 Mathews has been placed at the disposal of the writer, who, while 

 differing in some particulars from their conclusions, has found their 

 results of great assistance in reducing the labor of investigation. 



Geographic and Geologic Relations. 



The crystallines of Cecil county are part of a broad belt of meta- 

 morphosed sedimentary material and intrusive igneous formations, 

 which extends along the Atlantic coast from Alabama to Maine and 

 northward. 



This belt, trending northeast and southwest, forms the plateau 

 region on the eastern foot of the Appalachian district. 



In A T ew England the belt is well developed. In ^Tew Jersey the 

 formations are largely concealed beneath a covering of Triassic de- 

 posits. In Pennsylvania and Maryland the materials of this belt are 

 again well exposed through the removal of a large part of this 

 covering. 



The determination of the age, origin and structural relations of 

 these formations has long been a serious problem to geologists. 



In ]\ T ew England detailed investigation by Pumpelly, Emerson, 

 Dale, Wolff and Hobbs has resulted in the determination of Cam- 

 brian, Lower and Upper Silurian series of quartzites, marbles, schists 

 and gneisses, resting upon a protruding pre-Cambrian gneiss. 



In Pennsylvania Cambrian and Silurian quartzites and crystal- 

 line limestones have been determined in the western half of this belt, 

 while the structure and age of the gneisses of the eastern half are 

 still problematical. 



A natural division is manifest in the Piedmont belt of Maryland, 

 as in Pennsylvania. The western half of the belt contains formations 

 which are plainly of sedimentary origin, though nonfossiliferous and 

 " semicrystalline," and have been placed (provisionally) in the Cam- 

 brian-Silurian periods. 



The formations of the eastern division present more obscure 

 problems in origin and age. They have undergone such complete 

 metamorphism as to obscure or obliterate all evidence of origin or of 



