227 
The Rev. D. Williams also has communicated two papers re- 
specting these disputed rocks, which he refers to the transition 
or grauwacke system, and endeavours to show that the strata of De- 
vonshire can be distinguished into certain groups by their litholo- 
gical characters. 
Mr. De la Beche in his map of Devon and Cornwall, published 
in 1839, has adopted divisions of the strata, similar to those of Pro- 
fessor Sedgwick and Mr. Murchison, as to their order of sequence ; 
applying, provisionally, to the culmiferous rocks the name of Car- 
bonaceous series, and to the Devonian and Cornish slates the appel- 
lation of Greywacke. 
We know also on the authority of Mr. De la Beche that tin mines 
are worked in carbonaceous rocks at Owlescomb near Ashburton, 
on the east side of the Dartmoor granite, and on its west side at 
Wheal Jewel near Tavistock. He further informs us that one of 
the richest tin mines now worked in Cornwall, namely the Charles- 
town mine, east of St. Austle, is in a fossiliferous rock containing 
Enerinites and corals, and that the same corals occur also near tin 
mines at St. Just; and in the neighbourhood of Liskeard the Rev. 
D. Williams has found slates which contain vegetable impressions, 
dipping under other slates which are intersected by lodes of tin and 
copper. 
From these new facts, we learn that the killas and other slate 
rocks of Cornwall and the south of Devon do not possess the high 
antiquity which has till lately been imputed to them; and that tin 
occurs, as copper, lead and silver have long been known to do, not 
only in slate rocks that contain organic remains, but even in the 
coal formation. 
Soon after the publication of the views of Messrs. Sedgwick and 
Murchison, a similar change was applied by Mr. Griffith to the 
south-west portion of his geological map of Ireland. In a paper 
that accompanied the presentation of this map to us on 22nd of 
May last, he states that he has now coloured, as old red sandstone 
and carboniferous limestone, extensive districts of the counties of 
Kerry, Cork, and Waterford, previously considered of higher anti- 
quity ; imputing his former erroneous opinion to the identity in 
lithological character of the shales and grits of the old red sand- 
stone and carboniferous systems, with the older rocks in the transi- 
tion series, 
