. Geological Society, 323 



GEOLOGICAL SOCIETY. 



[Continued from p. 241.] 

 June 18, 1862. — Professor A. C. Ramsay, President, in the Chair. 



The following communications were read : — 



1. " On the Mode of Formation of some of the River-valleys in 

 the South of Ireland." By Professor J. B. Jukes, F.R.S., F.G.S., 

 of the Geological Survey of Ireland. 



Mr. Jukes's paper contained a description of the physical struc- 

 ture of that part of the South of Ireland south of the limestone-plain 

 that extends from Dublin to Gal way Bay. He showed that the 

 Rivers Shannon, Barrow, Nore, and Suir, after traversing this low 

 ground, escaped to the sea by ravines worn through lofty hills of Old 

 Red Sandstone and Lower Silurian rocks. He also instanced the 

 Rivers Blackwater, Lee, and Bandon as each suddenly deserting the 

 low longitudinal valleys through which they had run for many miles, 

 and turning at right angles down ravines of Old Red Sandstone, 

 notwithstanding the fact of the longitudinal valleys being continued 

 with no apparent obstruction to the course of the rivers. He showed 

 the connexion of these lateral ravines with the coming of strong 

 brooks from the higher ridges on the north into the longitudinal 

 valleys, and also that these brooks probably produced the ravines, 

 having first begun to erode them over a surface above the present 

 ridges, and before the formation of the longitudinal valleys. 



He considered the fact proved, that the present " form of the 

 ground" in the South of Ireland was produced by atmospheric ero- 

 sion on dryland, and that the limestone ground was low because the 

 rock had been dissolved chemically as well as eroded mechanically, 

 and that its surface had sunk to a lower level than the other rocks, 

 like that of a glacier melting in its bed. He proposed to extend 

 this explanation generally to all dry land. 



2. "Experimental Researches on the Granites of Ireland. — 

 Part III. On the Granites of Donegal." By the Rev. Professor 

 S. Haughton, M.A., F.R.S., F.G.S. 



The author described in detail the geographical position, physical 

 structure, geological relations, and the chemical and mineralogical 

 composition of the granite of Donegal, which consists of four mine- 

 rals — quartz, orthoclase, oligoclase, and black mica, with perhaps 

 an unknown paste besides. The oligoclase affords evidence of the 

 probable identity of the granite of Donegal with that of Northern 

 Scotland and of Norway. The author also alluded to his success in 

 obtaining a formula for the determination of the proportions of four 

 minerals in a compound rock, from the relative specific gravities of the 

 mass and of its constituents. 



3. " On a Stalk-eyed Crustacean from the Coal-measures." By 

 Professor T. H. Huxley, F.R.S., Sec.G.S. 



This specimen, in an ironstone nodule, is crushed laterally, and 

 exhibits a side view of a Crustacean, similar in all essential respects 

 to Pygocephalus. The chief interest attaching to the specimen lies 

 in the confirmation which it affords of the author's interpretation of 



