2 BONNEY : ON THE ORIGIN OF THE BRITISH TRIAS. 
and the third is sometimes uncomformable with the first. But, 
though I tliink these two represent very distinct chapters in 
the physical history of Britain, I would not like to assert that 
no part of the Muschelkalk had a time equivalent in our islands. 
The Keuper deposits, speaking in general terms, may be 
followed continuously from the South Devon coast to the Mid- 
lands, whence they extend along both sides of the Pennine 
Range, on the eastern to beyond the Tees, and on the western 
to North Lancashire. Here they come to the sea, but may 
then be traced through the Isle of Man to the neighbourhood 
of Carlisle on the one hand and the north-east of Ireland on 
the other. In Scotland also, outlying patches of that age occur 
on the north-eastern and western coasts. The Bunter, however, 
as we shall see, is absent from the more southern pr.rt of the 
Midlands, its " beds, in fact, form a wedge, lying diagonally 
across the central counties, with the apex pointing towards 
the mouth of the Thames."* It is again found in the south- 
west, where deposits of that age are exposed on the coasts of 
Devon and thin out in similar fashion towards the north and 
east, disappearing in the former direction before reaching the 
Bristol Channel. 
The following facts must be taken into account in any 
attempt to picture the physiography and climate of the Trias 
in this part of Europe. Speaking of the Bunter group first, we 
find that it also very often admits of a triple sub-division, 
namely, into the Lower Sandstone, the Pebble Beds, and the 
Upper Sandstone. The first of these deposits, usually uncon- 
formable with the Permian beds below, occupies a more restricted 
area, at any rate in the western Midlands, than the second. 
Putting aside its representative in northern Lancashire, about the 
identification of which there has been some dispute, we can trace 
it from the estuaries of the Mersey and Dee southwards along 
the borders of Wales and Shropshire. Near Liverpool it is 
about 400 feet thick ; in the neighbourhood of Bridgenorth 
it attains the unusual amount of about 650 feet. A fault near 
Bewdley forms its southern limit, but it thins rapidly both 
* Hull, Permian and Trias (Survey Memoir), p. 61. 
