88 Correspondence. 



tion and ice action. The Trappean rocks of the County Limerick 

 are naturally harder than the associated Limestone, therefore, as the 

 land rose, and came under the influence of Marine denudation, the 

 Limestones would have been much more rapidly worn away, leaving 

 the Trappean rocks standing up as Skerries, Carricks, and Carrickgeens ; 

 and also when the country was covered with ice, they would have 

 resisted its grinding action much more than the Limestone. Similar 

 results would occur in the hills of the N.W. of the County Gal way, as 

 the Granites and Altered Traps are naturally harder than the Gneiss 

 and Schist, and the Vein Quartz than the Quartzite. Some of the 

 Limestones were naturally harder than the Schist and Gneiss, but 

 not all; therefore some parts of it project above the other rocks, while 

 other parts were cut away equally with the Gneiss and Schist. 



Yoixrs truly, 



G. H. KiNAHAN. 



OUGHTERAKD, IRELAND. 



ON THE DENUDATION OF SOUTH AFRICA. 

 To the Editor of the Geological Magazine. 



Sir,— That part of the interior of South Africa extending from the 

 eastern slopes of the Zwartebergen and Zuurbergen, and the con- 

 tinuous chaiu of hills which dies out on the sea-coast, near the mouth 

 of the Qualana Eiver, to beyond the Vaal Eiver, and from Bean, far 

 west to some undetermined line a long way to the north of Faure- 

 smith, is occupied geologically by a series of nearly horizontal beds 

 of hard Sandstone, Clays, and Marls, intersected by numerous dykes 

 of Greenstone, Syenite, and Basalt. These strata contain, throughout 

 their whole extent, as far as it is known at present, numerous bones 

 of Eeptiles, stems of Calamites, leaves of Glossopteris and other ferns ; 

 shells of a species of Iridina, and some Fish with heterocercal tails 

 have been found at Fort Beaufort, Spitzkop, and elsewhere. All 

 these remains concur to prove that Mr. Bains' conjecture that these 

 beds were of lacustrine origin is correct. No fossil of any kind, 

 even possibly marine, has yet been found in them. Professor Owen 

 inferred, from a pretty extensive series of reptilian bones and fish 

 remains, that the age of the formation corresponded nearly with the 

 Triassic of Europe. 



Now, with the exception of a few beds of Eecent or Tertiary Lime- 

 stones, where the Lacustrine strata reach the sea-coast, there is no 

 evidence of any part of this formation having been covered by the 

 sea at any time siuce the desiccation of the lake ; and, therefore, it is 

 clear that the denudation which the country has undergone is not 

 due to marine action. It may, I think, be safely inferred, that had 

 the ocean rested upon these strata sufficiently long to produce any 

 serious amount of denudation, some beds of rock, containing sea-shells, 

 would have been left. The action of Glaciers may, I think, be left 

 out of our estimate of denuding forces, considering the latitude, and 

 probably not very great elevation of the country. The denudation 



