66 



Cincinnati Society of Natural History. 



This explanation of the abundant inclusions in the granite, 

 as it approaches the gabbro, brings them, on one hand, into a 

 kind of relation with the basic segregations described above, 

 while it allies them to definite foreign inclusions on the other. 

 In so far as they are early secretions of one great magma 

 they resemble the former, while their relation to the latter 

 consists in the fact that they must have been sufficiently 

 solidified at the time of their inclusion to act essentially like 

 rigid masses. 



Diorite. 



• This type is not present in any great amount, but it is 

 represented in several belts of hard, black rock, near Port 

 Deposit, extending in a north-east direction, parallel to the 

 foliation of the granite-gneiss. That the number of these 

 more basic belts is really greater than is indicated by those 

 found in place, is shown by the large number of diorite blocks 

 scattered over the - fields. In the northern part of the area 

 • only one band of this dark rock was noted, and this was 

 located near Harrisville. 



If these diorite belts are projections from the gabbro mass 

 at the north, and from the " Stony Forest" region of Har- 

 ford County at the south-west, which have been completely 

 changed through metamorphism, then these altered dykes 

 furnish evidence that the granite in these areas is older than 

 the gabbro, and also older than the granite in the neighbor- 

 hood of Rowlandville and Porter's Bridge. 



Staurolitic Mica Schist. 



One and one-half miles south of Liberty Grove an interesting 

 belt of rock was observed, which was traced for a distance 

 of two miles from the river in a north-east direction. This 

 rock is of a gray color, weathering brown, and it is composed 

 mainly of mica and quartz mingled with red, dodecahedral 

 garnets, which are covered with green chlorite. This schist 

 is squeezed and crumpled into minute plications. Its best 

 exposures are seen in the narrow valley of Basin Run, w 7 here 

 the boulders are filled with completely altered staurolite 



