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ON THE GEOLOGY OF CALDERDALE. BY JAMES SPENCER. 
{Communicated January 16th, 1894.) 
After describing the general aspects of the country through 
which the Oalder flows, the author enumerates the formations found 
in Calderdale. The strata of this valley and its tributary dales 
belong to the Carboniferous System, the Coal Measures, Millstone 
Grit, and Yoredale Beds being alone exposed, whilst the Mountain 
Limestone underlies the valley at no great depth. The total thick- 
ness of these strata exposed in Calderdale is from 4,000 to 5,000 feet. 
In order to obtain some idea of the physical geography of the 
Carboniferous period it is advisable to consider the condition of 
things at the beginning of the Devonian period. Then the area now 
occupied by the British Isles was girdled by a broad belt of Archsean, 
Cambrian, and Silurian rocks, which stretched from Scandinavia 
round the western coasts of Scotland, Ireland, and Wales. From 
this ancient north-western continent three elevated tracts of land 
stretched across what is now England and Scotland. The northern 
range ran across the Lake District, the middle tract across Shrop- 
shire and Leicestershire, and the southern range passed in an easterly 
direction from the Bristol Channel, then turning southwards and 
crossing the English channel, was probably continuous with the 
Ardennes Mountains. These high lands were acted on by extensive 
denudation, and the enclosed low-lying ground was filled up in the 
Old Red Sandstone period by thick beds of conglomerate, sandstone, 
shales, and volcanic ashes and lavas, in some places amounting to 
10,000 feet in thickness. The denudation of these strata probably 
furnished much of the material of the Calderdale rocks. At the 
close of the Old Red Sandstone period the whole area began to sub- 
side, and this downward movement continued, but with occasional 
pauses and slight upheavals, during the whole of the succeeding 
period. At the beginning of the Carboniferous period the sea 
extended from the middle of England through Derbyshire, Lancashire, 
and West Yorkshire, up to Central Scotland, but Northern Scotland was 
