19 
THE EVOLUTION OF THE CALDER RIVER 
SYSTEM. 
(Illustrated by the Lantern). 
By A. WILMORE, B.Sc., F.G.S. January 28th, 1908. 
The basin of the Lancashire Calcler is a well-defined one, 
and is roughly horseshoe shaped. It is bounded by the hills 
of the Pendle Range on the north-west and north, by the 
great moorlands stretching from Black Lane Ends to Crow 
Hill on the east, and by the Boulsworth and Hambledons 
on the south-east and south. It is open to the Valley of the 
Ribble by the well-marked and beautiful Whalley Gorge, 
but there is also low land through Rishton and towards 
Blackburn, which represents a former direction of discharge 
of the Calder drainage. The key to the structure of the 
basin is furnished by the dual series of earth-folds which are 
so conspicuously seen in this part of the mid-Pennines. The 
great east to west fold of the Pennine axis, with the north 
to south extension, gives the dominant direction of flow of 
the Calder system as one from east to west, for the various 
streams drain off the axis towards the Lancashire plains 
and the Irish Sea. The other direction of folding has its' 
axis from north-east to south-west, and, consequently, the 
actual arches and troughs are crossed along a line at right- 
angles to this, viz., from south-east to north-west. These 
folds are crossed as one proceeds, say, from Whitewell to 
Black Hambledon. The effect of the two systems of folding 
has been to make a trough or basin which is now drained by 
the Calder River system. The rocks concerned in all this 
folding are, of course, the various members of the carboni- 
ferous system, though there is some reason to suppose that 
newer rocks once formed part of the folded system, and that 
they have since been denuded away. 
In the immediate Calder River basin the coal-measures 
and the underlying millstone grits are the rocks concerned, 
and the way these rocks lie has been a most important factor 
