399 



Chalk. — This formation is extensively displayed resting in hori- 

 zontal strata on the highly inclined beds of mica-slate, and is for the 

 greater part overlaid by basalt. No additional characters, to those 

 already published, are given by the author, but he points out that the 

 boundaries which have been hitherto assigned to it are far from cor- 

 rect. 



Trap. — The history of this rock, the author says, has been so com- 

 pletely investigated in all its relations, that he has no new facts to 

 communicate regarding it ; he, however, notices the occurrence of 

 several important dykes, some of which pass through the conglome- 

 rate beds of the new red sandstone, without penetrating the strata 

 which rest upon them. 



Lastly, the author alludes to the enormous extent to which the 

 chalk and superincumbent basalt have been denudated in this por- 

 tion of Ireland, leaving only four isolated monuments within the area 

 of the district, to prove their former extension over the whole of its 

 surface ; and he enumerates several instances of the rapid destruc- 

 tion of the cliffs along certain portions of the coast, and of the accu- 

 mulation of detritus at the mouths of all the rivers. 



May 1 6. — James Mitchell, Esq. of New Broad Street, was elected 

 a Fellow of this Society. 



A paper " On the Geological Relations of the stratified and un- 

 stratified Groups of Rocks composing the Cumbrian Mountains," 

 by the Rev. Adam Sedgwick, V.P.G.S. F.R.S. Woodwardian Professor 

 in the University of Cambridge, was read. 



Chap. I. — Introduction. 



The author first shows, that the limits of the region to be described, 

 are defined by a zone of carboniferous limestone, based here and 

 there upon masses of old red conglomerate. This zone is described 

 as entirely unconformable to the central system, and for the pheno- 

 mena presented at the junction of the two great classes of rocks, he 

 refers to previous memoirs read before the Society. 



The rocks of the central system are separated into stratified and 

 unstratified j and the stratified are divided into four distinct groups, 

 in the following descending order : 



1 . Greywacke and greywacke-slate ; the whole group based on 

 beds of limestone and calcareous slate, and bounded at its upper 

 surface by a part of the carboniferous zone. 



2. A great formation of quartzose, chloritic, roofing slate and fel- 

 spar porphyry ; alternating in great, irregular, tabular masses, each 

 passing into, or replacing, the other ; the whole having nearly a 

 constant strike, and dip similar to that of the preceding group. 



3. Skiddaw slate — a very fine, dark, glossy clay-slate, occasionally 

 penetrated by quartz veins, sometimes passing into a coarse grey- 

 wac and greywacke-slate. 



4ke rystalline slates between the preceding group and the cen- 

 tral granite of Skiddaw Forest. 



It is then shown, that the mineralogical axis of the whole region 

 may be placed in the direction of a line drawn from the centre of 

 Skiddaw Forest to Egrernont, and that on the north side of this line 



