ABUNDANCE OF INCLUSIONS. 301 



At Woodstock similar irregular blocks of gneiss ;ire abundant in the 

 granite. 



Inclusions and their Contacts. — From Sykesville many inclusions have 

 been obtained in the granite a few rods below the railroad station, where 

 a quarry has been opened. Recently great quantities of the rock have 

 been removed for paving-blocks. During the progress of the work large 

 numbers of inclusions of foreign rocks have been brought to light in the 

 granite, furnishing indisputable proof of the eruptive origin of the granitic 

 mass at this locality. 



The inclusions found here consist of irregular fragments of all sizes and 

 shapes, from minute pieces up to blocks of large size. Among the various 

 fragments noted may be mentioned those which were evidently origi- 

 nally limestone, soapstone, pyroxenite, vein-quartz, hornblendic and 

 biotitic gneisses. Both with the naked eye and in thin slices under the 

 microscope characteristic contact phenomena are noticeable, similar 

 in all respects to those observed where molten rocks and calcareous 

 sediments or liquid lavas and certain crystallines have been brought 

 together. 



The inclusions derived from the limestone appear as thin yellow slabs 

 from one to several centimeters in thickness and of various sizes. Four 

 distinct zones are readily recognized, macroscopically, in the inclusions 

 of this class : (1) The median portion is tine-grained and lemon-yellow 

 in color. It is surrounded by (2) a narrow band usually 2 to 3 milli- 

 meters in thickness, white in color, and apparently composed chiefly of 

 minute grains of quartz. Then comes (3) a very small, fine-grained, dark- 

 colored shell of varying thickness, containing abundant small garnets up 

 to one millimeter in diameter. In many cases this layer is so thin as to 

 be scarcely noticeable. It shades off rather abruptly into (4) the typical 

 granitite of the area. 



Microscopically the four zones are even better differentiated : 



The first of these zones is found to bea typical lime-silicate hornstone ; 

 the second is made up almost entirely of fine, allotriomorphic quartz, 

 while the third belt is a fine-grained mixture of quartz and biotite, with 

 small garnets. 



Beside the limestone fragments there are abundant inclusions of soap- 

 stone, vein-quartz, biotitic and hornblendic gneiss. All of these rocks 

 are well represented several miles to the eastward of Sykesville, where 

 they dip to the west at a considerable angle. In the case of the two 

 latter especially, the outside is usually changed considerably for a dis- 

 tance of about one centimeter. The interior of the gneiss pieces is practi- 

 cally unmetamorpbosed. It is much lighter in color than the contact 



