886 Proceedings of the British Association. 



central portion of that county," by Professor Sedgwick and Mr 

 Murchison. — The authors began by observing, that this was a mere 

 outline of a more detailed memoir on the physical structure of De- 

 vonshire, which they were about to lay before the Geological So- 

 ciety of London. In the published geological maps of that county, 

 the whole system of the older slate rocks was represented under 

 one colour, without any attempt at subdivision ; and one colour al- 

 so represented different limestones, without any discrimination. 

 The object of the authors was, to remedy these defects, — to ascer- 

 tain and represent the true position of the successive deposits and 

 their natural subdivisions, so as to compare them with correspond- 

 ing deposits in other places. They also wished to determine the 

 true place of the remarkable carbonaceous deposits of central Devon, 

 which had been previously regarded as belonging to the lowest por- 

 tion of the grauwacke formation. A section was exhibited of part 

 of that county, from the north coast to one of the granite peaks of 

 Dartmoor immediately south-west of Oakhampton. A diagram of 

 the Section will be found in the opposite page. 



In the ascending order this section exhibits — 1. A system of 

 slaty rocks, containing a vast abundance of organic remains, gene- 

 rally in the form of casts. These rocks sometimes pass into a fine 

 glossy clay-slate, with a true transverse cleavage ; sometimes into a 

 hard quartzose flagstone, not unusually of a reddish tinge ; sometimes 

 into a reddish sandstone, subordinate to which are beds of incohe- 

 rent shale. In North Devon they are very rarely so calcareous as 

 to be burnt for lime, but in South Devon, rocks of the same age 

 appear to be much more calcareous. 2. A series of rocks charac- 

 terized by hard thick-bedded red sandstone, and red micaceous flag- 

 stone, subordinate to which are bands of red, purple, and variegat- 

 ed shales. The red colour occasionally disappears, and the forma- 

 tion puts on the ordinary appearance of a coarse, siliceous grau- 

 wacke, subordinate to which are some bands of imperfect roofing 

 slate. In this series are very few organic remains. It is several 

 feet in thickness, occupying the whole coast from the west end of 

 the Valley of Rocks to Combe Martin. 3. The calcareous slates 

 of Combe Martin and Ilfracombe, of very great aggregate thick- 

 ness, abounding in organic remains, and containing in a part of their 

 range at least nine distinct ribs of limestone burnt for use. This 

 limestone is prolonged into Somersetshire, and appears to be the 

 equivalent of that on the flanks of the Quantock Hills — 4. A for- 

 mation of greenish and lead-coloured roofing slate of great thick- 



