224 SUPERFICIAL DEPOSITS. 



submerged during some part of the quart ernary period. Both 

 islands present a series of well washed raised beaches, the 

 highest yet noticed in Guernsey being about 76 feet, and the 

 highest in Jersey 125 feet at its lowest part above mean tide 

 level, while the rolled stones found in the clay on the high 

 plateau ground of both islands give reason to believe that the 

 submergence was greater than that indicated by the raised 

 beaches, and that both islands were entirely, or almost entirely, 

 under water. The yellow clay or brick earth of the islands 

 was, I think I am safe in saying, formerly considered by most 

 if not all geologists to have been produced in situ by the 

 subasrial decomposition of the rock on which it lay, and in 

 places spread out by rain wash. 



When I endeavoured to show in a paper read before the 

 Geological Society* that this could not be true of at least a 

 very great part of the clay, and that it was mostly, if not 

 entirely, an aqueous deposit, my views met with little accept- 

 ance. In some of the higher parts of the island it has seemed 

 to me that the clay, or at least its lower portion, is the result 

 of in situ disintegration, and very possibly it was all originally 

 produced by the decomposition of local rocks ; but there can 

 be no doubt that most of it has been carried and deposited 

 where it is now found lying. This is shown by the fact that 

 the clay may be found lying on perfectly undecomposed rock, 

 on blue clay, and on the raised beaches ; and also by its con- 

 taining fragments of rocks other than that on which it rests. 

 That it is an aqueous deposit, one laid down by or under water 

 is, I think, shown by its rounded grains, by the stratification 

 it occasionally exhibits, and by its sometimes including raised 

 beaches or parts of them, and containing rolled waterworn 

 stones. Also, the position of some of its contained blocks, 

 held up at an angle, and the occurrence of layers or beds of 

 rock fragments seem to me to strengthen and confirm the other 

 evidences of aqueous deposition. The view that the clay was 

 deposited under water, or that water, in one way or another, 

 was the agency by which it was transported or spread out, 

 would probably be generally accepted, but the exact mode of 

 its deposition, and the conditions under which it was distri- 

 buted, as well as its precise geological date, appear to me to 

 be questions which are very far from being settled. 



The moving force which spread it out over slight slopes 

 and level ground must have been a powerful one, or one in- 

 volving more than aqueous transport pure and simple. As we 

 have seen, some of the large blocks it contains have been 

 * " On the Jersey Brick Clay." Quarterly Journal Geological Society, Feb., 1889. 



