DAVIS: SOURCE OF BOULDERS IN CALDER VALLEY. 153 
been accounted for in a variety of ways ; but the one I now 
suggest — that they were the shores of the old sea — perhaps 
appears the most reasonable when considered in connection 
with the drift deposits filling up the base of the valley. If 
they are the remains of the shores of an old lake, as some 
authors have described them to be, there remains the 
difficulty of damming up the waters to so great a depth, 
which does not appear probable, and of which there is no 
evidence at present existing. 
In conclusion, the evidence that the erratic boulders in 
the valley of the Yorkshire Calder were derived from the 
sources so plentifully supplied in the great valley occupying 
the whole of the centre of the county, rather than from the 
district westwards of the summit of drainage, appears 
conclusive. In the one case we have the source of the 
Calder bounded by a series of hills rising to a height of 
1,500 feet or more, and the only openings being at Calder 
Head on the northern and at Hollingworth on the southern 
part of the Chain. In either of these the land rises rapidly 
from the Lancashire side to the height of 610 feet and 700 
feet respectively, and in each case they form the summit of 
drainage. All evidence proves that the general form and 
direction of the valleys remains unchanged since pre-glacial 
times, and this being so, the ordinary action of rivers being 
the agent which has carried the boulders from the Lancashire 
districts over the summits of drainage may be dismissed as 
out of the question, and, along with it, the theory of some of 
the early geologists, of a great wave of translation which 
was supposed to have swept across , the Atlantic to our 
shores, and was made answerable for every unaccountable 
phenomenon in surface geology presented to their notice. 
A more probable theory is that they were carried over by 
icebergs ; but this necessitates that the land be submerged to 
the depth of 700 or 750 feet, and, if that be granted, there 
