%0 Dr. Mac Culloch's Account of Guernsey^ 



also be traced gradations into mere quartz ; and I further observed 

 some varieties consisting of wavy mixtures of quartz and hornblende 

 only. 



This stone has a considerable tendency to decomposition, the fel- 

 spar and mica being both very ferruginous. It is consequently 

 found in all states, from that of a friable rock, to a gravelly clay, 

 and finally to a perfect soil ; constituting the gravelly or sandy loam 

 which predominates through the Island. 



No where is it more easy to remark the process by which in 

 nature rocks are converted into earth ; and as in this case by the 

 action of an oxide of iron. Nests of yellow mica which seem to 

 have arisen from the decomposed rock, are found in many places. 



This stone is used for rough masonry. 



A ledge of rocks called the Hanois extends from the westernmost 

 point of the island, and from its apparent geographical continuity 

 is probably of the same structure. Against this point the whole 

 strength of the western ocean is first directed. And it is from hence 

 I doubt not, that a large ridge of rounded masses of stone has been 

 rolled, so as to form a natural barrier near Rocquaine. 



In quitting the elevated part of the island, and with it the southern 

 shore, the gneiss disappears ; and its place is supplied by other 

 granitic formations. Besides the trap and trap porphyry which I 

 remarked at Rocquaine, there are masses of micaceous schist, having 

 the appearance of veins ; and a stratum of argillaceous schist may 

 also be observed at the lower parts of the bay, incumbent on the 

 granitic foundation. 



At I'Eree and Lihou the rocks are composed of quartz and felspar, 

 the foliated texture having disappeared. A granitel is thus formed, 

 which in some places receiving an addition of hornblende, passes 

 into sienite. This is traversed here and there by veins of the same 



