TRANSACTIONS. 
77 
throughout its whole course, the conclusion of the writer is, that 
this bed of Basalt w as produced by an overflowing of lava during 
the deposition of the Mountain Limestone Group, after those 
beds, which are found below, and prior to those above it. 
After Mr. Hutton’s paper had been read, 
Mr. Murchison rose to bear testimony to the general value 
and accuracy of the memoir. His own observations, however, 
on the evident violence which in High Teesdale accompanied 
the arrangement of the basaltic matter, the altered character 
of the limestone, sandstone, and shale both above and below it, 
and the occasional ramification of its substance through the con¬ 
tiguous and superior Strata, led him to confirm the opinion of 
Professor Sedgwick, that the Whin of that district had not been 
injected into the Carboniferous Limestone till after the deposi¬ 
tion of that whole system of rocks. He thought it very desira¬ 
ble that the views of Professor Sedgwick respecting the Whin 
Dykes of Durham should be further pursued, with reference to 
this theory, to ascertain whether they were emanations from the 
great Whin Sill, or were posterior to it. Some of these Dykes 
break off into various branches, all pointing to the Whin Sill, and 
thus appearing at least to be related to it in age. 
Mr. Phillips had formerly examined the whole range of the 
Whin Sill, and was happy in being able to agree in opinion with 
both the author of the paper, and the President of the Geolo¬ 
gical Society. The definite geological situation, between the 
same Limestone bands, of the great portion of the Basalt, its 
wide lateral extension, the general limitation of the effects of its 
heat upon the contiguous rocks to the lower surface of the mass, 
its course for miles together without furnishing a single dyke, or 
even entering at all into the many natural fissures of the Lime¬ 
stone, and its division by metallic veins, obliged him to infer that 
a large portion of the Whin Sill was formed by periodical sub¬ 
marine eruptions of Lava, at intervals during the deposition of 
the Carboniferous Strata with which it is associated. On the 
other hand, the instances described of violent eruption and local 
intrusion of the Basalt into the Strata above its general range, 
seemed to show that Teesdale had been the theatre of more 
than one such eruption. The views of Professor Sedgwick and 
Mr. Hutton were, therefore, by no means irreconcileable ; and 
it might be very possible hereafter to fix upon the foci or centres 
from which, as probably at Caldron Snout in Teesdale, the 
principal basaltic coulees had flowed. 
