284 Proceedings of the Royal Physical Society. 
Upper New Red. The evidence afforded by the Bristol 
area does not stand alone in this respect, but is abundantly 
confirmed by the relation of these rocks to each other in 
many different areas. 
More than that, in Devonshire the New Red Rocks over- 
step not the whole of the Carboniferous, but most, if not the 
whole, of the Devonian Rocks as well. Possibly this latter 
feature may be attributable to an unconformity between the 
Upper Old Red and the Devonian Rocks, similar to that in 
Ireland between the Upper Old Red and the Glengariff Grits, 
and in Scotland between the Upper Old Red and all the 
rocks older than itself, including the Orcadian Old Red and 
the Caledonian Old Red. 
If we assume that this unconformity in the Bristol area repre- 
sents the removal of 15,000 feet of strata at the rate of 1 foot 
in 5000 years, that adds 45,000,000 years to our chronology. 
Time required for the Formation of the Carboniferous Rocks. 
—Speaking in very general terms, the Carboniferous Rocks of 
England and Wales may be said to be divisible into two 
sections— Upper Carboniferous, which in Britain is certainly 
a terrigenous deposit, formed at no great distance from the 
land, probably as part of a delta; and Lower Carboniferous, 
which in England, Wales, and Ireland, is certainly in the 
main a marine deposit formed in moderately deep water in 
the southern parts of the kingdom, and in shallower water 
in Scotland. In some districts where fossils have not yet 
given the clue, there exists a little uncertainty as to where 
the dividing-line between the Upper and the Lower division 
should be drawn. In other districts, both physical and 
paleeontological evidence point to the existence of an uncon- 
formity between them, as there is a very marked discrepancy 
between the vertebrate faunz of the two divisions,! and the 
discrepancy between the fossil floras is not less pronounced.? 
For the present purpose, it will suffice to regard the rocks of 
the Severn basin as fairly typical of the whole series, and to 
base our estimates upon the facts we can glean from a study 
1 Traquair, Proc. Roy. Soc. Edin., vol. xviii. (1890), p. 387 ; Geol. Mag., 
Dee. iii.; vol. i., pp. 115-121. 
2 Kidston, Proc. Roy. Phys. Soc., 1894. 
