Paleo-Geological and Geographical Maps of the British Islands, 277 
conglomerate formed of pebbles of Carboniferous Limestone. The Alberbury 
breccia belongs to this formation.* 
Distribution of Land and Water.—lt is probable that during the Lower Permian 
period two distinct basins were formed, lying on either side of the dividing ridge, 
both being inland lakes, or only very slightly connected with the sea. Into these 
lakes were carried beds of fine sand, clay, and gravel by the streams draining the 
adjoining lands formed of older Palzeozoic rocks. On the commencement of the 
Upper Permian period there was a subsidence over the region of the northern lake, 
and the waters of the sea flowed in, bringing with them representatives of a marine 
fauna, and in which the ereat limestone beds of the north of England were 
deposited. These beds are not represented over the centre and west of England, in 
which the beds belong exclusively to the lower division of the Permian system, 
known in Germany by the name of “ Rothe todte liegende.” 
Puate XXX. 
The Triassic Period. 
The terrestrial movements, accompanied and followed by extensive denudation 
which ensued at the close both of the Carboniferous and Permian periods, produced 
marked changes in the distribution of the strata of the Triassic period as compared 
with that which preceded it. There is a complete discordance between the 
Mesozoic and the Upper Paleozoic strata, so that the beds of the New Red Sand- 
stone, or, in its absence, those of the Keuper Marl, rest indifferently on various 
members of the Permian, Carboniferous, or even older rocks. 
Amongst the physical changes brought about at the close of the Carboniferous 
period, was the formation of a ridge of Paleeozoic rocks, under the south of 
England, of which the Mendip Hills is the western prolongation, and against which 
both on the north and on the south the Mesozoic strata wedge out. Under the 
east of England, this ridge is in part composed of the older Silurian or Cambrian 
beds which occupied that district during the Carboniferous and Permian times ; but 
it was considerably extended at the close of the Carboniferous period, and forms a 
portion of that great system of flexured and folded strata which range from the south 
of Ireland, through the south of England and Wales, into France and Belgium, and 
beyond the Rhine. Another ridge of great importance in physical geology is of 
that known as the “ Back-bone of England,” which ranged from Derbyshire 
northwards, and was developed at the close of the Triassic epoch. It is formed of 
Carboniferous rocks. 
As I showed some years ago, the Triassic strata attain their greatest develop- 
ment in Lancashire and Cheshire, and become attenuated in a south-easterly 
direction. This is due partly to the position of the old Paleozoic ridge above 
* Murchison, “Silurian System,” p. 83 
