650 Professor Sedgwick and R. I. Murchison, Esq., on the 



read before this Society*) are fine examples of what we are here stating, and 

 many others are exhibited in the interior of the district. In spite of this confu- 

 sion, we easily ascertain that the limestone rocks of Tor Bay and Berry Head 

 belong to the highest strata of the older formations on the south-eastern side of 

 Dartmoor. Now the limestone series at Berry Head (both from the evidence 

 of the coast section and from the evidence of the section along the estuary of 

 the Dart) is found to plunge under the slate region, which is expanded through 

 the great south promontory. From which it follows, that a section first from 

 Dartmoor to Berry Head, and then continued from Berry Head (coastwise) to 

 Start Point, must cross all the old stratified deposits of South Devon. We think 

 there is no doubt that the Plymouth limestone is exactly or very nearly the 

 equivalent of the limestone of Berry Head. Hence (after what has been said 

 respecting the strike and dip of the country) it must be obvious, that a trans- 

 verse section from the granite of Dartmoor to the Plymouth limestone, and 

 then continued from that limestone (coastwise) to Bolt Head or Start Point, 

 would also give a nearly perfect series of the strata of South Devon. We 

 examined the several lines above-mentioned ; and in the essential details of the 

 corresponding pans, they appeared to agree perfectly, some of the lowest beds 

 only being wanting on the line from Dartmoor to Plymouth, Our hmits pre- 

 clude minute details ; but we will, in a few words, endeavour to describe 

 the facts which are exhibited on those lines of section, and seem essential to 

 our classification. 



1. — Sections from the east side of Dartmoor to Berry Head, 8^0. ^c. 



Commencing with the section from Dartmoor to Torbay, we pass over the stratified rocks im- 

 mediately in contact with the granite ; for in that association, whatever part of the series they 

 may belong to, (and under this remark we include the culm-measures as well as all the older for- 

 mations,) they become so entirely metamorphic as to lose all their distinctive characters. But at 

 a little distance from the granite, (for example, on the north side of Ivy Bridge, and on the east 

 side of a line drawn from Ugborough to Buckfastleigh) there are extensive tracts of a rock which 

 deserves notice. It is hard, brittle, and porcelaneous ; sometimes passing into a compact fel- 

 spar, sometimes into a flinty slate or Lydian stone, not unusually resembling the well-known 

 altered coal-shales in contact with trap dykes. We have no doubt that these rocks have been in- 

 durated by the action of the granite, as in following them in the ascending order, they graduaUy 

 pass into the common dark-coloured roofing-slate of this country. Higher in the ascending sec- 

 tion, the slates become calcareous, and here and there pass into masses of bluish gray limestone. 

 Two or three distinct bands of this kind may be seen in the neighbourhood of Ugborough ; and in 

 the range of the strata northwards, the calcareous portions unite into one leading mass, and swell 

 out so much as to make, in the neighbourhood of Ashburton, a great feature in the district. The 



* See Mr. De la Beche's Memoirs, Transactions of Geological Society, 2nd Series, vol. iii. 

 part 1, p. 160. 



