CLASSIFICATION OF OUR ROCKS. 63 
the fragments putting on a decided slaty texture 
and feel, but still displaying the presence of lime 
on application of the test—these facts conjointly 
pointing out the coeval deposition of the whole. 1t 
is however requisite to state, that sandstone is not 
only blended with fossiliferous slate, but also at 
times with blue dunstone, (indurated slate) which 
is not fossiliferous, and I have seen fossiliferous 
lime situated between beds of “ grey dunstone” also; 
so that, it will be necessary in theorizing on the 
question of the deposit of these several strata, to 
admit that dunstones are coeval with the other 
rocks notwithstanding their deficiency of organic 
remains,* or, for the sake of apparent consistency 
towards the doctrine of separation of fossiliferous 
from non-fossiliferous rocks, to admit the perplex- 
ing and inconsistent idea of different ages of 
dunstones, according to the positions they assume 
with respect to other rocks, as also, to allow similar 
separations of other non-fossiliferous slates from 
such as do contain fossils. In fact, if we are to 
apply this classification of rocks according as they 
contain petrifactions or not, some sandstones will 
be classed with the fossiliferous slates and lime, 
and some with non-fossiliferous slates, trappean 
rocks, &c. ; the true greywacké rock will be separ- 
ated from the greywacké slates ; some beds of lime 
must be separated from others, and even some parts 
of a given bed from the rest ; the dolomite blended 
as it is with true limestone will not be coeval with 
that formation ; in some instances, the general mass 
of a hill, or bed of slate must be ranked differently 
from that part which is fossiliferous though seem- 
* T have lately found, that there is an exception to the rule of 
grey dunstone being devoid of fossils, in the case of a portion on 
the shore at Mount Batten apparently connected to the metalife- 
rous shale before spoken of. 
