158 Geological Society. 



2. " On the older Rocks of South Devon and East Cornwall." 

 By Harvey B. Holl, M.D., F.G.S. 



The author divided the rocks of the district to which the com- 

 munication referred into a Lower, Middle, and Upper South-Devon 

 Group, and stated that the lowest beds were brought up along a 

 line of country extending from Dartmoor by Kingston Down to the 

 Brown Willey granite, where they formed a broad anticlinal axis. 

 These rocks are unfossiliferous, and may not be lower in the series 

 than the base of the Ilfracombe group of North Devon, or the highest 

 part of the group immediately below it, the latter being more pro- 

 bably represented by some still lower beds of red and greenish grits 

 brought up to the surface in the anticlinal axis of St Broeck's Down 

 further to the west. 



The Middle South-Devon Group comprises at its base the discon- 

 tinuous calcareous range of the Looe River, St. Germans, Brickfort- 

 leigh, Ashburton, and Bickerton, above which is a mass of blue and 

 claret-coloured slates, which separate it from the Plymouth or Tor- 

 bay Range. 



This calcareous and fossiliferous group is succeeded by higher 

 beds of blue and claret-coloured argillaceous slates, followed by 

 hard, red, dark, micaceous schists, and purple and greenish grits, 

 which constitute the author's Upper South-Devon Group. These 

 rocks are very sparingly fossiliferous, and probably correspond to the 

 upper and Morthoe portions of the Ilfracombe series of North 

 Devon. 



The unconformable position of the Culm-measures is seen in the 

 circumstance that they rest upon different parts of the underlying 

 Devonian rocks— sometimes on the limestones of the Torbay range, 

 sometimes on the slates, at others on the volcanic rocks. This 

 entirely separates the South-Devon rocks from the Carboniferous 

 system. 



The occurrence of the genus Ptei^aspis, and probably Cephalaspis 

 with Phrjllolepis concentricus and (?) Holoptychius, and other fish- 

 remains, appeared to the author to go a good way towards identifying 

 these Cornish and South-Devon beds with the Old Red Sandstone 

 of Scotland. These fossils range up to the very base of the Torbay 

 limestones. 



The author referred the whole of the rocks treated of, with the ex- 

 ception of the purple and greenish grits of St. Broeck's Down, to the 

 Middle Devonian system, and considered that if the lower or Linton 

 rocks were to be met with at all on the south side of the Culm- 

 trough, it would be in the high ground which forms the watershed 

 of West Cornwall. 



In the concluding portion of the paper Dr. Holl entered upon the 

 palaeontological relations of the different South-Devon groups, and 

 especially those of the Petherwyn beds. 



