85 
DYKES, MINERAL VEINS, &c. 
vast area to the beds above and below. To me both these observations 
appear of great importance, and it seems clear that the basaltic lava 
spread over the bed of the sea at intervals, during the deposition of a 
portion of the carboniferous limestone, that in certain places its eruption 
was accompanied by some violence, but no where directed by so im- 
mense a force as one capable of opening horizontally the whole lime- 
stone series for many square miles. Such an inconceivable force must 
have filled every fissure of all the rocks from Middleton to Hartley 
burn, with dykes of basalt, ranging in all directions, while in fact almost 
nothing of the kind is known, and even around Caldron snout, only 
very small mechanical effects are due to the Whin, and these are, as far 
as I have seen, wholly confined to the subjacent beds. 
It is not necessary to suppose that only one such submarine flow 
of basalt occurred, any more than to confine it to one opening; the 
double or triple Whin beds of Northumberland, sufficiently counten- 
ance a belief, that the region was often disturbed by such eruptions. 
It is remarkable that the alteration of limestones and shales is 
most conspicuous near Caldron snout, where the mass is greatest ; it is 
in this part only, that the strata are much changed above the Whin; 
and it is perhaps the only locality for perfectly granular limestone. If 
we suppose a deposition of limestone to happen upon the bed of the 
sea, some time after the production of the melted rock beneath, the 
natural result would be a change of the limestone, only or principally 
where the mass of igneous rock was very great ; in all other places 
the necessary heat would have escaped. 
If this reasoning be admitted to prove the Whin sill to be of the 
same geological period as the attendant strata, it follows that the dykes 
are wholly independent of it, and posterior to it, though doubtless 
derived from the same plutonic focus. 
Other Dykes . — "Besides the dykes already mentioned in connection 
with the Whin sill, I am acquainted with only two in Yorkshire. 
