190 
GENERAL VIEWS. 
The millstone grit series grows thin round the north side of the 
Cumbrian slate mountains ; this does not appear to be the case on 
the south side ; portions of it are thick in Derbyshire, but in all 
the southern parts of England and Wales, and in Belgium and West- 
phalia, the whole series is reduced to obscure and unimportant traces. 
In the North-West of Ireland it is considerably developed, but in Arran 
and Scotland hardly known at all. 
These observations appear to prove that the agencies concerned in 
producing the millstone grit series were not geographically posited 
like those which occasioned the grits and shales of the Yoredale 
rocks ; but not sufficient to justify any further speculation on their 
origin. 
Time elapsed. 
It is too difficult a problem for the present state of geology to 
determine the length of time which was consumed in the produc- 
tion of any given set of rocks : upon particular suppositions, com- 
parative results might indeed be obtained, as I have shewn in the 
Encyclopaedia Metropolitana, but these speculations belong to general 
not local geology. 
Depth of Ocean. 
This is another very interesting branch of inquiry too obscure to 
be followed out with any reasonable hope of success, except in a 
general discussion of geological theory. Too little is known of the 
distribution of recent organic forms in the sea, to justify the adoption 
of general rules, relating to the depth at which they live : and even 
were this not the case, the almost total dissimilitude between recent 
species and those of the mountain limestone would prevent our applying 
them. No certain conclusion can be drawn from the nature of the 
deposits, though, compared with other formations they appear to in- 
dicate considerable depth, and, unless from general views concerning 
the elevation of the strata from the bed of the sea, there appears 
at present little hope of throwing real light on this matter. 
