550 Notices of Memoirs—W. W. Watts—Hornblende, ete. 
by them in the year 1877, were not accepted by the chiefs of the 
Geological Survey ; but in the year 1891, in his anniversary address 
to the Geological Society, Sir A. Geikie admitted that the rocks 
in this ridge, “variously termed quartz porphyries, felsites, and 
rhyolites,” were not intrusive in the Cambrian rocks, as marked on 
the Survey Maps, but “the oldest members of the volcanic series,” 
and that “there is no true passage of the sedimentary rocks into it; 
on the contrary, the conglomerates which.abut against it are in great 
part made out of its fragments, so that it must have been already in 
existence before these Cambrian strata were deposited.” 
The grits and slates which overlie the conglomerates in these 
areas have always been classed by the Geological Survey as Lowest 
Cambrian ; therefore any attempt on the part of the Geological Survey 
to extend the term Cambrian so that it might include the much older 
rocks which the surveyors had incorrectly marked as intrusive, and 
‘chiefly of Lower Silurian age,” the author thinks is unwarrantable. 
The error which caused the surveyors to class other pre-Cambrian 
rocks as “‘altered Cambrian” equally renders it impossible to group 
those with the Cambrian, especially as in no instance has it been 
shown that the so-called “altered Cambrian rocks” have their 
equivalents amongst the unaltered Cambrian rocks of the Survey. 
Moreover, it is certain that there is a marked unconformity at the 
base of the Cambrian (unaltered Cambrian of the Survey) in all 
the areas in Wales where the beds are seen to rest on the rocks 
classed by the author and others as of pre-Cambrian age. 
Il.—Norses on a Horneuenpr-Prkrite From Greystones, Co. 
Wickiow. By W. W. Warts, M.A., F.G.S. [Communicated 
by permission of the Director-General of the Geological Survey. | 
J iis this paper the author gave a description of a rock which forms 
a dyke in the Cambrian slates and grits of Greystones, in Co. 
Wicklow. It is a dark, dense, coarsely-crystalline rock, showing 
large crystals of hornblende with lustre-mottling, owing to the 
weathering-out of olivine crystals. It becomes finer-grained at the 
margins. An analysis by Dr. Sullivan was added. 
The hornblende is of the usual green type, and occurs in large 
crystals enclosing pseudomorphs of olivine, now made up of 
magnetite and probably a colourless amphibole. A colourless 
hornblende also occurs either as cores or borders to the green 
erystals. A third type of hornblende present shows few cleavage 
cracks and much magnetite dust. Apatite is a constituent, but there 
is no felspar in the rock. The margin of the dyke is much sheared 
and phacoidal in structure. 
IiI.—Norss on tHe Perurric Quartz Grains In Ruyourre. By 
W. W. Warts, M.A., F.G.S. [Communicated by permission of 
the Director-General of the Geological Survey. | 
HE author exhibited specimens of that variety of the Sandy 
Braes Rhyolite from County Antrim which was formerly called 
Perlite. A microscopical examination of the rock shows crystals 
