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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



where. The Upper Devonian beds were first determined by myself 

 at Messrs. Menx's ; they are of the true N. Devon and N. Cornwall 

 Devonian type — dark chocolate-coloured semi-slates containing the 

 characteristic shells Spirifera disjuncta and ffliynchonella cuboides 

 &c. This discovery solved the problem of the existence of Palaeozoic 

 rocks at an accessible depth under London, and of the absence of 

 the Jurassic series. Immediately above the Devonian occurred the 

 Lower Greensand, abnormal in all conditions save the never- failing 

 test of fossil remains, and what few occurred left no doubt as to the 

 age of this at first somewhat doubtful rock. Trigonia alceformis, 

 Cardium Hillanum, Trochoeyaihus Harvey anus, and Gerithia, &c, 

 added to the general facies, immediately settled the question of age ; 

 neither of the other four borings exhibited any signs of the true 

 Lower Greensand. At Ware and Turnford the Gault rested upon 

 from 8 to 10 inches of theCarr stone, and this was all that represented 

 the Neocomian rocks beyond the 65 feet of chalky oolitic subcal- 

 eareous abnormal Lower Greensand ; all the borings show that the 

 Neocomian (Lower Greensand) is interrupted on the north by the 

 underground Palaeozoic ridge. The geographical extent or surface- 

 area occupied by the Devonian of North Devon between the Pilton 

 beds on the south and the Linton beds on the north (15 miles), 

 where we believe we have the full thickness of the whole series, is 

 as near as possible that known to occur between London and Turn- 

 ford, assuming that the strike of the North-Devon beds is directly 

 towards the London area, and thence on towards Belgium and the 

 Rhine (Eifel and Coblentz). The Devonian cores brought up at 

 both localities (Tottenham Court Road and Turnford) yielded the 

 same characteristic fossils ; and the beds dipped at the same angle 

 at both places, 30° S.E. — the plane of the old land-surface being 

 1148 feet below London, and 980 feet below Turnford, showing a dif- 

 ference in level of 168 feet, due either to dip or denudation. I should 

 believe the difference was due rather to denudation along or over a 

 given plane striking from S.W. to N.E. Where the junction of the 

 Upper Devonian and Wenlock rocks may take place between Turn- 

 ford and Ware it is difficult to say ; but if we infer that the Ludlow 

 and Lower Devonian beds occur above the Wenlock, dipping south 

 between Ware and Turnford, then there is little room for them, and 

 the Upper Devonian must cease at no great distance north of Turnford. 

 Looking at the thickness of the Lower Devonian in North Devon, and 

 regarding it as maintaining the same in its strike under Wiltshire, 

 Buckinghamshire, Middlesex, and Hertfordshire, there is room in 

 the 8 miles from S. to N. at the dip of 30° S. for the presence of the 

 Lower Devonian and Ludlow. We need not assume that the Lud- 

 low beds do occur, any more than we should expect to find the great 

 sandy and gritty group of the Foreland, whatever it may repre- 

 sent. The old land-surface, therefore, of Devonian and Old Red 

 Sandstone of the southern half of England must have extended from 

 near Yarmouth (lat. N. 52° 30'), descending by a gentle southerly 

 curve to about Leighton Buzzard, thence lising to the Wenlock pro- 

 montory, and again sharply deflected S.W. to Milford Haven, and 



