916 PROFESSOR J. PRESTWICH ON THE EVII>ENCES OF A SUBMERGENCE 
and covers the highest parts of the islanch It likewise has been referred to disintegra¬ 
tion of the rock in situ, or to rain-wash. But as I have explained in describing 
Guernsey, the height at which it occurs, precludes the possibility of its being rain- 
wash, while though superposed on the disintegrated rock surfaces, the absence of the 
quartz grit of decomposed granite or syenite, and the presence of angular rock 
fragments or rubble at its base,* * * § equally show its special and independent origin. This 
was the opinion of Professor Ansted,! who says “In addition to the soil derived fi’om 
the decomposition and disintegration of the rocks in all the island, there are occasional 
deposits of some extent of brick-earth and potter’s clay.” It is also the opinion of 
Dr. A. Dunlop,| who found that in one place the brick-earth had a thickness of 50 
feet. No Mammalian remains have been found in these drifts, which tends to confirm 
the early separation of the islands from the mainland. 
Similar phenomena are exhibited on the French coast. M. Tribolet§ says that, on 
the small island of Brehat on the north coast of Brittany, there are deposits of loam 
about 2 feet thick, overlying the granite, “ completely identical with those which are 
known in Switzerland and Germany, under the name of Loess.” It there contained a few 
land shells {Pupa, Helix, Succinea, &c.), with the small concretions termed race, so 
common in Loess. M. Tribolet found the same Loess on the adjacent mainland, and 
supposed that it might have been deposited by the water descending from small 
glaciers on the inland hills, but these are of small height and show no sign of glacial 
action. The other reasons I have applied to the Channel Islands witli respect to its 
special and local origin, apply equally to the island of Brehat. 
One feature that I failed to notice in Guernsey occurs in marked distinctness in 
Jersey. This is the distance to which the “head” has been propelled from its base. 
The section at the islet of La Motte is even more illustrative than that at Godrevy 
in Cornwall, which I have before described, j] This islet lies mile south-east of St. 
Heliers, on a part of the coast where the shore is low, but rising gradually inland to 
a height, at Mont Ube, of 149, and at Prince’s Towmr, 2-^ miles inland, of 200 feet. 
A rubble-drift descends the slopes of Mont Ube and St. Clements (160 feet) and forms 
a small low cliff on the coast, while at the distance of about 1000 feet from the shore, 
and accessible at low water, is the small, flat islet of La Motte. It is only a few 
acres in extent, and consists of a base of diorite, capped by the remains of an old 
beach, overlaid by a mass of rubble-drift or head, the section of which is very similar 
to that represented in fig. 8. It consists of— 
* At Copp’s brickfield I found one to tliree feet of angular rubble under several feet of brick-earth, and 
at the base decomposed granite in situ. 
+ ‘ The Channel Islands,’ p. 296; see also pp. 279-295. 
+ ‘ Quart. Journ. Geol. Soc.,’ vol. 45, p. 118, 1889. 
§ ‘Ann. Soc. Geol. du Norcl,’ vol. 5, p. 100, 1878. 
II ‘ Quart. Journ. Geol. Soc.,’ vol. 48, p. 281. 
