226 Reports and Proceedings. 



to have been percolated by solutions carrying tbe products of tbe 

 alternation of such minerals, it was suggested that the reduction to 

 the metallic state was mainly produced by the action of substances 

 contaiaing protoxides of ii'on, which by higher oxidation have given 

 rise to the dark-red colour and the earthy ochreous substances found 

 in the vein-matter. The causes producing the metalliferous deposits 

 in the trap were stated to have evidently acted throughout the 

 whole system, and the absence of copper from the compact beds is, 

 probably, rather due to the absence of cavities fit for the reception 

 of such masses, than to any difference in chemical composition. 



The following specimens were exhibited : — Copper-ores from the 

 State of Michigan ; exhibited by H. Bauerman, Esq., F.Gr.S. A 

 piece of an iron water-pipe, containing a calcareous incrustation 

 deposited from the water supplied to the City of Bath ; presented 

 by John Lawson, Esq., C.E., E.G.S. 



Edinburgh Geological Society. — March 1st, 1866 — David Page, 

 Esq., F.E.S.E., F.G.S., Vice-President, in the Chair.— Mr. D. J. Brown 

 read a paper " On the section of the Mid-Lothian Coal-field at Shaw- 

 fair," and Mr. G. C. Haswell read the first part (introductory) of a 

 paper " On the Crustacea of the Silurian beds in the Pentland Hills." 



March 22nd, 1866.— E. A. E. A. Coyne, Esq., C.E., in the Chair. 



1. Mr. George Lyon gave a short sketch of the " Geology of the 

 Cowgate." 



After alluding to some of the more prominent archgeological features 

 of the Cowgate, he stated that the hollow, in which this now extinct 

 suburb of the city stands, is the result of the denudation of the Castle 

 Rock, the denuding agent having scooped out two parallel and con- 

 verging valleys, one on each side of the great central ridge on which 

 the old town is built, — that which forms the Cowgate, being about sixty 

 feet higher than the other which formed the Nor' Loch, now Princes 

 Street Gardens, and the reason why this ridge is so sharp and well 

 defined, arises from the soft nature of the rocks, principally shales, 

 on which the denuding agent acted. The excavations recently made 

 for the New County Buildings, laid open a section of the Boulder 

 clay about twenty feet deep, in which were imbedded several boulders 

 which had been transported by currents of water from the Castle 

 Eock. Proceeding in a direction towards the Advocates Library, the 

 pick and spade laid open the foundation and walls of old tenements 

 and a thick mass of rubbish, containing bones of animals, shells of 

 the oyster, cockle, and mussel, which showed that the inhabitants of 

 former times deposited their refuse heaps at their doors, and the 

 kitchen -midden must have been a prominent feature in the back 

 alleys and garden enclosures. 



The Cowgate never seems to have been a loch like its congener 

 which now forms Princes Street Gardens. It probably existed only 

 as a marsh. The drainage of the Cowgate, some years ago, opened 

 up a larger section of the Boulder clay to the depth of about nine 

 feet ; no marl was found. Several trap dykes exist along this line of 

 denudation which strike through the strata in a direction contrary to 

 the dip. 



