PEEBLE COUNTY. 413 



gradual thickening of the bowlders until we find them in the central 

 part of Washington township so numerous as to render the tillage of the 

 fields difficult. From this point the belt can be followed in a broad band 

 to the south-eastward as far as to the county line and even beyond. Its 

 length within the county will thus be seen to be at least ten miles. Its 

 greatest breadth does not exceed three miles, but the east-and-west roads 

 of the county cut across it diagonally so as to show sections of four or 

 five miles in breadth. 



The bowlders range in size from one thousand cubic feet downwarda 

 Of one hundred and two blocks that were lying on the surface within a 

 small compass, the greatest length in any bowlder was seven feet. A 

 second gave a measure of five feet; four exceeded four feet; six exceeded 

 three feet ; thirty-five measured more than two feet, while the balance 

 (fifty-five) were under two feet, none being counted that were less than 

 one foot. It is probable that within the same area there were nearly as 

 many more concealed by a shallow covering of soil. On the farm of 

 David Potterf, near west Alexandria, 1,200 bowlders exceeding two feet 

 in diameter were counted to the acre. There are points where they are 

 certainly more numerous than this. The value of the land is dimin- 

 ished where it is so thickly covered, the expense of raising and removing 

 them being considerable. 



The bowlders lie upon or very near to the surface. Numerous sections 

 of the Drift beds in this district are furnished in the banks of streams 

 and in artificial cuttings, but they do not disclose any unusual number 

 of these blocks at any great depth. 



In their distribution they are irrespective of the elevations and irreg- 

 ularities of the surface. They cover the high ground and the low im- 

 partially. The central portions of the belt occupy a part of the great 

 northern plain of the, county, which has an altitude of about one thou- 

 sand feet above the sea. 



There is a considerable variety of composition among them. The 

 kinds most largely represented are named below, in the order of their 

 abundance : 



1. Metamorphic slates, fine-grained, and very hard ; in color, dark blue, red- 



dish, and green. 



2. Dioiites, blue and green, frequently intersected by felspathic veins. 



3. Silicious conglomerates, excessively hard, whitish, light green, and purplish. 



4. Gneiss, two leading varieties, viz., orthoclasio or red-banded, and horn- 



blendic or black-banded. 



5. Granites of the ordinary types, many of the blocks intersected by felspathic 



veins, which often stand out in relief from the weathering surfaces. 



6. Porphyries, comparatively rare, some with white felspar crystals, but more 

 ' withreddish crystals. 



