I4 PROCEEDINGS COTTESWOLD CLUB 1904 
and subsequently identified by Murchison as Cambrian, is 
now proved by the Geological Survey to be Precambrian, 
and is called the Torridonian. It rests transgressively 
upon the Hebridean gneiss, with no formation intervening. 
Dr Hicks found in this newer Precambrian group included 
fragments of “greenish, purplish, and reddish slate, schist, 
jasper, etc., similar in many respects to those found in 
the Cambrian conglomerates of Wales,” which he con- 
sidered were derived from his Pebidian series. The 
Geological Survey later on described a conglomerate from 
the Torridonian, which'contained, amongst other varieties, 
‘well-rounded pebbles of slaggy porphyrite,” a well-known 
volcanic rock. There is therefore good reason to believe 
that in the Scottish area there once existed a volcanic 
formation older than the Torridonian, and therefore of 
approximately the same age as the Uriconian. This is a 
remarkable example of the proof of a geological formation 
from the sole testimony of derived fragments in a younger 
group. 
It would be unprofitable to attempt correlation between 
our English Uriconian and any external group of racks. 
In several Irish localities, such as Howth Head, Wexford, 
and County Donegal, I have seen strata which bore a close 
resemblance to the slaty type of the Uriconian, and they 
were probably of Precambrian age. Volcanic rocks below 
the Cambrian are well-known in America. They occur in 
both the Lower and Upper Huronian, and later on they 
form enormous masses in the Keweenawan ; but in the 
absence of fossil evidence we cannot affirm the exact 
contemporaneity of any one of these groups with the 
Uriconian. It is, however, interesting to note that in 
America, as in Britain, the periods preceding the Cambrian 
were marked by great and varied volcanic energy. 
The doctrine of uniformitarianism receives striking 
confirmation from the Uriconian rocks. The lavas and 
