Dr. Mac CuLLOCH o;2 Ouartz RocL 453 



view of large tracts. In many parts of the shore, however, the 

 disposition of the strata is evidently changed, and they are ob- 

 served occupying every possible variety of position, from the 

 horizontal to the vertical. The steps by which these changes 

 succeed each other eluded my observation, and perhaps are not to 

 be traced. 



I will now describe the principal modifications which this rock 

 tissuraes, so as to give an idea of its mineralogical character, before 

 I attempt even to conjecture its place in a geological system. 



It exhibits the following varieties : 



1. An extremely compact granular stone, consisting of grains of 

 quartz, of unequal sizes, united without cement. 



2. The same, containing grains of clay, which appear to be 

 decomposed felspar. 



3. The same, with more numerous grains of felspar, which 

 appear on examination generally to consist of rounded fragments. 



These rocks are traversed by veins of quartz, of which the 

 aspect is also granular, but they are distinguished from the body of 

 the rock by their snow white colour. They often appear so 

 incorporated with the rock that the line of separation cannot be 

 distinguished. 



4. A similar rock containing angular grains of quartz of half an 

 inch in diameter, and bearing every mark of having been formed 

 from a disintegrated granite, except that it exhibits no traces of 

 mica. 



5. The same rock containing a flattened oval pebble of quartz,, 

 perfectly smooth, and having uniform curved surfaces, as if from 

 long attrition. The pebble is two inches in length, and one and a 

 half in breadth. It was so firmly united to the rock, that on one 

 side it has been broken in the attempt to separate it. 



