442 CO. T. Clough—The Whin Sill of Teesdale. 
the Whin. It would be a very laborious task to prove that the Whin 
is so uniform in composition as asserted, but I think that we may 
conclude that it probably is so, from its general mineralogical 
uniformity and the results of the few analyses that have been made 
of it. Some time ago I got analyses of two samples of Teesdale 
Whin executed in Dr. Percy’s laboratory: one sample was taken 
from the top of Widdy Bank Fell, where I thought a mass of lime- 
stone had probably been absorbed by the Whin, and the other from 
the neighbourhood of Forest Church, where it seemed more likely 
that sandstone, shale, and limestone, in about equal proportions, had 
been absorbed. It will be seen from the appended details that the 
two samples are essentially the same chemically just as they are 
mineralogically :— 
Basalt from Tinkler’s Syke, top of 
Basalt from Teward’s Bridge, near 
Widdy Bank Fell. Forest Church. 
Composition Composition 
per cent. per cent. 
Silica ... 51°47 | Silica ... 50°35 
Alumina Sie TOAST Alumina eee eee meee 16°80 
Protoxide of Iron 8:49 | Protoxide of Iron ... ... 8°36 
Peroxide of Iron iss 3°61 | Peroxide of Iron ae 3°51 
Protoxide of Manganese ... 0:46 | Protoxide of Manganese ... 0-41 
Lime ... auyits 8-22 | Lime ... uc eeeee 9°01 
Magnesia 5°10 | Magnesia ... 5°73 
Potash 3°28 | Potash 2°87 
TSEC ea velee ia bey eee ne eee sacsts laa! Gal Meee KT ISKODE, Naas Pmmecriac,. 1L20)7/ 
Tron 0:08) +. : 2 Tron 0:037 : 5 
Sulphur 0-09 f Tron Pyrites 0°17 Sulphur 0-043 \ Tron Pyrites 0:08 
Hygroscbpic 0°50 Hygroscopic 1°20 
Take i : : : 
Water } GeShined 1-20} 170 | Water { Combined 0°80 \ ee 
100°16 100-19 
Specific Gravity 2°82 Specific Gravity 2°84. 
But any force which this objection possesses depends upon the as- 
sumption, that if sedimentary beds were taken up by the Whin they 
would remain in it close at hand to their original situation, whereas 
there may have been a very general circulation, both on a large scale 
and molecule by molecule, reducing all the parts of the mixture to a 
general uniformity of composition. The very possibility of forming 
alloys and of modifying the properties of metals by adding to them 
small portions of other substances depends upon this principle of 
circulation or diffusion, so that it cannot be said that we are without 
warrant for it. And, whatever theory of the formation of igneous 
rocks we adopt, it seems necessary to suppose that there has been in 
them such a circulation at some time or other, when they were ina 
molten state, for otherwise how can their uniformity of character 
over large areas be accounted for? We may suppose them to have 
been made at a time very far back indeed—to be contemporaneous 
with the “beginning of the world” —or we may suppose them to 
he of much later date; but in either case we must suppose that 
there was some kind of general circulation or diffusion through their 
mass bringing them down to an uniform composition, as far as 
consistent with their physical surroundings. 
