20 



THE GEOLOGIST. 



siderable depth, from which large quantities of sand are continually 

 carted for the purposes of ballast or manure. Other sections, similar 

 to the above, are to be found further inland, the most interesting of 

 which is that in a pit by the side of the road on the Green leading 

 towards New Quay. The stratum of sand there is not, it is true, more 

 than six inches thick, but lying, as it does, under about eight inches 

 of soil, upon one of the highest points in the island, the section is 

 valuable, as showing that, in all probability, at one time, the whole of 

 the surface of the island has been capped with sand, which has been 

 washed away from those portions where it is now deficient, leaving the 

 underlying stratum of brown clay visible. The section in this pit I 

 estimated as follows : — 



Surface Soil, 8 inches. 



Fine White Sand, 6 inches. 



Brown Clay, 2 feet. 



" Ram," or coarse grit, 7 feet. 



Granite. 



The stratum No. 3 prevails very widely over the whole island, 

 coming to the surface in all the lower lands, and forming the great 

 bed in which agricultural and gardening operations are carried on, 

 I traced it completely across the island to Tolman Point in one 

 direction, and to Watermill Cove in the other. Its dark colour is in 

 all probability due to the large proportion of oxide of iron which it 

 has derived from the chemical decomposition of the mica of the disin- 

 tegrated granite. No. 4 is a very instructive bed as developed in the 

 various sections in which it is brought to light. It gives a thorough 

 insight into the mode by which the apparently solid granite has in 

 the course of ages been broken up and crumbled, and thus gradually 

 submitted to the action of the elements, until its constituent parts 

 have been resolved into strata serviceable to man. In many places 

 within these islands, may be traced the several stages of decomposi- 

 tion, from solid masses of granitic rock, to broken fragments, thence to 

 crumbling rubble, and to coarse granitic sand, and the final passage 

 into aluminous and siliceous earth from the degradation and decompo- 

 sition of the felspar and quartz, in many places tinged deeply with 

 the oxides of iron from the decaying mica. That the islands have been 

 several times submerged, during the course of these successive changes 



