Reports and Froceedings — Geological Society of London. 125 



Geological Society of London. 

 I.— January 11, 1882.— E. Etlieridge, Esq., F.E.S., President, in 

 the Chair. — The following communications were read : — 



1. '•' On the Chalk masses or Boulders included in the Contorted 

 Drift of Cromer, their Origin and Mode of Transport." By T. 

 Mellard Eeade, Esq., F.Gr.S. 



The author referred to the occurrence in the Contorted Drift of 

 Cromer of large masses of chalk, and came to the following conclu- 

 sions : — The travelled masses are derived from sea-cliffs and the 

 result of landslips, aided by the penetration of water forming ice, 

 intrusive in fissures which detached them from the parent rocks. 

 Water rising from subterranean sources accumulated as ice around 

 the fallen masses, and was then frozen into the shore-ice. loe-tloes 

 brought into contact with these masses were also frozen into them, 

 forming a raft capable of floating away the boulders. The incline 

 of the shore and the rise and fall of the tides on the breaking up of 

 the ice would suffice to launch the rafts into the sea, and they 

 probably floated in water not more than 200 feet deep. The fre- 

 quency of these boulders and their accumulation in , the Cromer 

 deposit points to their having been arrested by the shoaling of the 

 water and by stranding on a submarine bank. The nature of the 

 chalk showed that they had not travelled far. 



2. " Observations on the two types of Cambrian beds of the 

 British Isles (the Caledonian and Hiberno-Cambrian), and the con- 

 ditions under which they were respectively deposited." By Prof. 

 Edward Hull, LL.D., F.E.S., F.G.S. 



In this paper the author pointed out the distinctions in mineral 

 character between the Cambrian beds of the North-west Highlands 

 of Scotland and their assumed representatives in the east of Ireland 

 and in North Wales. In the former case, which included the beds 

 belonging to the " Caledonian type," the formation consists of red or 

 purple sandstones and conglomerates ; in the latter, which included 

 the beds belonging to the " Hiberno-Cambrian type," the formation 

 consists of hard green and purple grits and slates contrasting strongly 

 with the former in structure and appearance. 



These differences the author considered were due to deposition in 

 distinct basins lying on either side of an Archaean ridge of crystalline 

 rocks which ranged probably from Scandinavia through the central 

 highlands of Scotland, and included the north and west of Ireland, 

 with the counties of Donegal, Derry, Mayo, Sligo, and Galway — in 

 all of which the Cambrian beds were absent, — so that the Lower 

 Silurians repose directly and unconformably on the crystalline rocks 

 of Laurentian age. 



As additional evidence of the existence of this old ridge, the author 

 showed that when the Lower Silurian beds were in course of forma- 

 tion, the Archaean floor along the west of Scotland must have sloped 

 upwards towards the east ; but he agreed with Professor Eamsajr 



