246 W. A. E. USSHER ON THE TRIASSIC 
in this paper may be succinctly stated in the four following pro- 
positions :— 
1. That the Triassic rocks of Normandy are a south-easterly pro- 
longation of the Devon and West-Somerset area, and bear somewhat 
the same relation to it as the Marls and Dolomitic Conglomerate of 
the Mendip area. 
2. That Keuper deposits alone are represented in Normandy, and 
apparently only the upper stage of that division. 
3. That from the foregoing considerations &c. there are strong 
grounds for concluding that fragments of the Norman paleeozoic rocks 
were never incorporated in the Triassic strata of Devonshire. 
4. That the constitution of the coasts of Normandy, Devon, and 
Cornwall is such as to justify the belief that varieties of Cambrian, 
Silurian, Devonian, and granitic rocks formed the bed of the 
Triassic waters in the area now occupied by the English Channel, 
and that to these sources fragments in the Trias of Devon, foreign 
to its soil, are to be attributed. 
The grounds on which I venture to propound these statements 
being, in many instances, common to more than one of them, it is not 
possible in every case to deal with the evidence for the propositions 
seriatim, without including under one head arguments applicable to 
others. 
First Proposition. 
The first proposition does not admit of positive proof, but is put 
forth on the strength of certain considerations and analogies, as 
follows:—First. The thickness of the Trias, with few local ex- 
ceptions, steadily increases from the Mendip area southward till its 
maximum, so far as can be observed, is attained on the South-Devon 
coast; so that it is likely that the prolongation of the formation 
would exhibit a still greater development in the area of the English 
Channel. 
Secondly. Fragments derived from sources foreign to Devon and 
Somerset appear in the gravelly beds of the Trias near the southern 
shores of the former county, preponderating at the expense of lecal 
materials from about twenty miles inland, till, on reaching the sea- 
board, 2 maximum increasé is exhibited. This seems to favour the 
idea that Triassic sediments not only extended far into the Channel 
area, but were there to a great extent formed from rocks different in 
character from those met with in Devon, and, in some cases, of older 
date than any to be found in the south-western counties. As, from 
the Budleigh-Salterton pebbles, we must conclude that Silurian and 
Devonian quartzites (and, not improbably, Cambrian strata) fur- 
nished material, either directly or, in part, in the form of paleozoic 
conglomerates *, one not unnaturally turns in the direction of the 
nearest land where similar rocks occur, not necessarily in the hope 
of finding a direct source, but of obtaining indices of the proximity 
of similar sources in the bed of the intervening Channel. Hence, 
* Mr. H. B. Woodward suggests that a conglomerate of Devonian age would 
furnish the requisite material. 
