DAVIS! SOURCE OF BOULDERS IN CALDER VALLEY. 145 
two valleys along which the railway lines run north-west- 
wards to Burnley and southwards to Littleborough. The 
watershed between Burnley and Littleborough is formed by 
a series of hills rising about 1,400 feet above the sea-level, 
extending from Shievely Pike and Heald Moor southwards 
to Tooter Hill and along Trough Edge to the summit near 
TTalsden. Throughout the whole of this district on the 
Yorkshire side of the watershed, with the exception of a 
small patch of gravel in Walsden, near the "Waggon and 
Horses public-house, there is no trace of gravel or drift. 
The beds of the several streams in Dulesgate, Howroyd 
Clough or Ramsden Clough, though deeply cut, exhibit no 
sections in which drift can be found. On the western or 
Lancashire slopes of the hills boulder clays and drift occur, 
often reaching a thickness of 150 to 200 feet. In excavating 
Hollingworth Reservoir, which is four or five miles west 
of the summit, and 568 feet above sea-level, extensive beds 
of gravels were found, which contained marine shells of the 
genera Fusus, Cardium, Purpura, Keritella, etc. Marine 
shells in the drift are not uncommon in other parts of the 
district. 
The Yorkshire and the Lancashire Calders rise near 
together at Colder Head. The latter is fed by many small 
tributaries which have their source on the slopes of the hills 
eastwards. These tributaries have formed deep valleys or 
cloughs, and exposed great thicknesses of gravel and boulder 
clay. Good examples may be seen in Cant Clough and 
Hurst wood Brook, near Worsthorn, and in the Catlow and 
Thursden Brooks. The boulders have been derived from 
the boulder clay, which still in many instances is found at 
the base of the drift. The latter is composed mainly of 
carboniferous limestones and sandstones, with an intermix- 
ture of Silurian grits, traps, quartzites, and granites. The 
carboniferous limestone occurs in such abundance that it 
