Juke8 — On the Gorge of the Awn. 445^ 



Let anyone travel through the country with Professor Eamsay's 

 geological map in his hand, together with the sheets published by the 

 Geological Survey, for details. Let him then look at the fretted and 

 gullied escarpment of the Oolitic range from Northampton to Somer- 

 set, and recollect (as shown by Mr. Topley in a former number of the 

 Geol. Mag.), that the sea does not form escarpments, but cuts sections. 

 Let him follow the level sheets of Lias and Trias, down the coasts of 

 Somerset and Glamorgan, till they abut against the Palaeozoic hills, 

 on both sides of the Bristol Channel. Eeturning to the Oolitic 

 escarpment of the Cotteswolds, let him mark how the Oolitic outliers 

 get fewer and smaller as he recedes from it, and let him connect 

 them with the broad outlier of Inferior Oolite, on Dundry Hill, five 

 miles south of Bristol, and the still more curious little patch of 

 it that caps the Lias peak of Brent Knoll, which rises from the flats 

 of Bridgewater. He cannot fail to come to the conclusion that not 

 only the Lias, but the Oolites, once spread in level sheets across the 

 district now occupied by the estuary of the Severn up to the Pale- 

 ozoic Hills of South Wales. 



The outlying patches of Lias that occasionally cap the red marls 

 through Warwickshire, Staffordshire, and Cheshire, prove that the 

 Lias, at least, formerly extended to, and wrapped round, the Paleo- 

 zoic hills of North Wales. 



Let the observer then stand on the highest point of Clifton Down 

 and look up to the superior height of Dundry Hill, some six miles 

 to the southward, and he would see at once that the extension of the 

 old Oolitic sheet would pass some two or three hundred feet over his 

 head. That the Lias itself rested directly on the Palgeozoic rocks is 

 shown by the fact of sheets of it still stretching across the Carboni- 

 ferous Limestone to the north-east of Durdham Down, still resting in 

 patches on the Backwell Hills to the westward of Dundry, and on 

 that of the Mendips, in the neighbourhood of Harptree. 



The Lias then formerly reposed on the Carboniferous Limestone 

 of Clifton Down and the Oolite spread over that. The Severn and 

 its tributaries, flowing over this Oolitic plain, of course cut channels 

 in it. The original form of the surface was such as to turn the Avon 

 towards the Severn instead of towards the Thames. The course it 

 originally took, it has ever since maintained, cutting down through 

 the horizontal Mesozoic cover, and through any Palaeozoic rock it 

 found underneath, in whatever position it might lie, or whatever 

 materials it might be composed of. Daring part of the time the 

 whole country must have been higher out of the sea than it is now, 

 and the rivers must have run as continuous streams over the land 

 which is now the bottom of the Severn estuary, till they had cut 

 down to the level where the solid rock would now be met with, 

 under the estuary mud. If the whole country got a hoist of one or 

 two hundred feet, the Avon would be a rapid brook at Clifton, fret- 

 ting over the rocks at the bottom of the gorge and continuing the 

 work of channel-cutting, which at the present level of the land it has 

 been obliged to suspend. 



While the rivers have been cutting their channels the rain and its 



