50 Prof. Sedgwick on the general Structure 



division of Cumberland called Millam. Thence it ranges through Corn Park^ 

 over the Knot, into the Low House grounds ; and, after crossing a marsh, 

 reappears in the same range above Water Blain, and terminates at the foot of 

 the village called Hill, — the mean bearing of the beds in the whole of this 

 range being about north-east by east, and the dip south-east by south. 



Here we lose all trace of the limestone ; but after ascending several miles 

 up a rivulet, we find, immediately above Graystone House, among the hills 

 to the east of Duddon Bridge, a bed of limestone, identical in dip and range 

 with the one we had left behind. Moreover, the Graystone House limestone 

 is very nearly in the exact prolongation of the band of transition limestone on 

 the other side of the Duddon, Hence we may conclude that the Graystone 

 House and Water Blain limestones belong to the same formation, and have 

 been severed by an enormous fault, descending nearly in the direction of the 

 valley of Hallthwaite. The quantity of dislocation estimated in the direction 

 of a perpendicular to the two parallel lines of bearing cannot be less than two 

 miles*. 



Such a disruption of great mountain masses is not a little startling to the 

 imagination; but I may state, by way of explanation, that many of the neigh- 

 bouring mountains are penetrated by dykes of porphyry and syenite, probably 

 of the date of the eruption of the Bootle granite, and that the whole region 

 of Black Comb, which belongs to the oldest slate formation, has probably at 

 the same period been thrust out of the bowels of the earth, and elevated into 

 a position out of all symmetry with the structure of the neighbouring region. 

 The country between Millam and Duddon Bridge is, therefore, one where we 

 ought to look for the evidence of enormous dislocations ; and this evidence is 

 placed before us in the most impressive manner by that break in the con- 

 tinuity of the limestone, and that great lateral movement which I have just 

 described. 



The beds of the Graystone House limestone would, in their prolongation, 



* It is right to state that there is a difficulty in identifying the Graystone House and Water 

 Blain limestone, arising out of the mineral character of the overlying slates. In general we can 

 easily separate, even by hand specimens, the greywacke slate of the highest group from the 

 green slate under the limestone. But at Graystone House this is not possible, as the overlying 

 slates are in structure almost identical with those of the inferior group. Hence some one might 

 conclude that the Graystone House limestone formed no part of the calcareous band described 

 above, but was an accidental mass subordinate to the series of the lower green slate. There is not, 

 I think, much force in the objection; for there are other places where portions of the two slate groups 

 cannot be mineralogically distinguished : and, after all, it merely shifts the difficulty, as we shall have 

 (on this supposition) to interpolate an enormous fault, somewhere on the line of the Duddon, in order 

 to explain the position of the corresponding calcareous bands on the opposite sides of the river. 



