, 182 
for, when he states, that in the metalliferous rocks of Tavistock 
tunnel, Redruth and St. Agnes, &c., he still recognises all the cha- 
racters of Wernerian clay-slate; and in the tract formerly coloured 
as greywacke, all the characters of that group as it exists in the Hartz, 
the district where the term originated, and to which therefore, in all 
cases of doubt, the geologist is bound to appeal in dernier ressort, as 
the true and undoubted type of the greywacke formation. Hence, 
continues Mr. Greenough, it becomes necessary to observe, first, that 
the characters which Werner assigned tu clay-slate are not confined to 
it; and secondly, that the old red sandstone has obtained admission 
into this part of his map only by a sacrifice of its independence, 
and upon condition of taking rank there, but as an integrant member 
of the greywacke formation. 
The term greywacke, if employed in a mineralogical sense, Mr. 
Greenough says, may safely continue to be used to designate that 
granular compound of semi-crystalline fragments cemented by 
clay-slate, found in rocks of every epoch in the Grampians, in Car- 
diganshire, the Tarantaise, along the whole range of the Alps, the 
Carpacks, the Apennines, &c.; in a geological sense, if employed at 
all, it should be strictly confined in its application to the Hircynian 
system and its equivalents. 
The English language, he adds, is rich enough to dispense with 
a word which has long since been objected to with reason as being 
harsh in utterance, as well as uncertain in signification, and therefore 
he thinks geologists ought to abstain from all further use of it. The 
phrase old red sandstone is equally superfluous. Therefore, he ven- 
tures to apply the designation of Upper Killas to the series of beds 
above the Silurian, and that of Lower Killas to the series below the 
Silurian. 
To the terms Devonian and Cambrian, Mr. Greenough entertains 
the following objections : 
1. If by Devonian system is to be understood only a part of the 
rocks of Devon, there is lost the only name whereby the whole can 
be designated. 
2. If this name be applied to denote the agreement of the Devon 
rocks with those of Herefordshire and other midland counties, the 
only name is lost whereby may be denoted (what is equally worthy 
of being denoted) their disagreement. 
3. The expression “‘ Devonian system” is just as applicable to 
the culmiferous beds of Devon as to the beds beneath them. 
4, The name of an English county is not a proper designation 
for an extensive European range. 
5. The title Cambrian system, according to its natural and ob- 
vious signification, should include all the rocks of the principality,— 
among others the very system to which it is opposed, the Silurian. 
Mr. Greenough then adverts to Mr. Bakewell’s including the 
old red sandstone and mountain limestone in the transition class, 
(Introduction to Geology, 5th edit. p. 135, 136,) and quotes at 
length Dr. Macculloch’s description of the old red sandstone as laid 
down in that author’s System of Geology (vol. il. p. 213, et seq.). 
This description, he says, characterizes in every important particular 
