in America and Europe. 277 
Britain had mapped as intrusive syenite, granite and felstone 
(petrosilex-porphyry) having Cambrian strata converted into 
crystalline schists on one side, and unaltered fossiliferous Cam- 
rian beds on the other. So long ago as 1864, Messrs. Hicks 
and Salter were led to regard these granitoid and porphyritic 
rocks as pre-Cambrian, and in 1866 concluded that they were 
not eruptive but stratified crystalline or metamorphic rocks. 
After farther study, Hicks, in connection with Harkness, pub- 
lished in 1867, additional proofs of the bedded character of 
these ancient crystalline rocks, and in 1877 the first named 
observer announced the conclusion that they belong to two 
distinct and unconformable series. Of these, the older consisted 
of the granitoid and porphyritic felstone rocks, and the younger 
of greenish crystalline schists, the so-called Altered Cambrian 
of the official geologists; both of these being overlaid by the 
region, which holds their ruins in its conglomerates. To the 
lower of these pre-Cambrian groups, Hicks gave the name of 
and also a reddish feldspar-porphyry which forms two great 
ridges in Carnarvonshire. ‘his latter was by Professor Sed 
Wick regarded as intrusive, and is moreover mapped as suc 
with the Dimetian and Pebidian of South Wales. 
r. Hicks continued his studies in both of these regions in 
1878,—being at times accompanied by Dr. Torell of Sweden, 
Professor Hughes and Mr. Tawney of Cambridge, and the 
schists and greenstones (diorites) of the Pebidian, and the 
older granitoid and gneissic rocks, there exists, both in North 
and South Wales, a third independent and intermediate series, 
Am. Jour. 8c1.—Turrp — Vox. XIX, No. 112.—Aprit, 1880, 
