Granites of Cecil County, in North-eastern Maryland. 81 



These crystals will be more fully described in the section on 

 batea separation. 



Sphene occurs in irregular masses without crystal form, and 

 also in the form of inclusions in the biotite. Its distribution 

 is limited, and it was only observed in a few granites near 

 Rowlandville and near the gabbro contact. 



Tourinaline and apatite are not abundant, the former is 

 rarely present, while the latter occurs as long, slender, broken 

 crystals in the diorites and hornblende granites, and in shorter 

 crystals in the other granites. 



BASIC FACIES. 



As the gabbro contact is approached there is a marked 

 increase in the basicity of the granite, which becomes darker, 

 and in some places it is difficult to separate from the gabbro 

 in the field. This is caused by the presence of hornblende 

 and magnetite, which were absent in the granites farther south. 



The hornblende occurs in green, strongly pleochroic crystals 

 of considerable size, with extinction angles varying from 

 nearly zero to twenty degrees, according to the direction of 

 its sections. It is filled with inclusions of magnetite, epidote 

 and zircon. This latter mineral is interesting, since zircon is 

 a mineral characteristic of the acid rocks, while it here occurs 

 in a basic mineral and in a basic facies of the granite. 



Magnetite, as proven by the magnet, becomes very abundant 

 near the gabbro line. It occurs in irregular masses, and only 

 rarely shows good crystal boundaries. It forms inclusions in 

 the different rock constituents, such as quartz, feldspar, mica 

 or hornblende, and often borders epidote, feldspar, biotite 

 and zircon. It is sometimes scattered evenly through the 

 rock in the form of small, more or less rounded grains, which 

 are very abundant. 



Secondary Alterations in the Rowlandvieee Granite. 



epidotization. 



Orographic movements and chemical changes have made 

 important additions to the minerals which composed the 



