110 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 7, 



similar rocks overlie the Greystone House limestone as far as the 

 borders of the estuary immediately below Duddon Bridge. This 

 fact is indicated in the colours of my field map exactly as I finished 

 this part of it in 1822, My examination during the past summer 

 enables me to answer this question in the affirmative. The lime- 

 stone^ though granular and crystalline, passes into ferruginous, cel- 

 lular, calcareous slabs with fossils ; and the whole development of 

 the group (with the exception of a partial mineral change caused by 

 the association with igneous rocks) is exactly like that of the Co- 

 niston limestone, and is very nearly on its line of strike, only a slight 

 deviation having been produced by the valley of the Duddon. 

 These alternations of fossiliferous and igneous rocks are anomalous 

 in this part of England ; but the very anomaly brings the formation 

 I am describing into more intimate comparison with the rocks of 

 the same, or nearly the same age in North Wales. Assuming the 

 truth of what has been stated, it follows that the limestone must 

 have been shifted by a vast fault and break of the whole series of 

 strata, more than two miles from its original strike. Those who have 

 studied the great dislocations of the strata near Coniston Water- 

 head will have little difficulty in admitting what is here stated*. 



The second question I wished to examine was this, — Is there in the 

 structure of the neighbouring county anything to explain this enor- 

 mous Greystone House fault ? I have already in another place 

 answered this question in the affirmative. Immediately to the west 

 of Greystone House, the rugged hills of green slate and porphyry 

 rise to an elevation of about 1500 feet, and are penetrated by dykes 

 of quartziferous porphyry (tt). Similar slates and porphyries are con- 

 tinued farther south at a much lower level, and their beds are shat- 

 tered in many directions : they then form the well-defined ridge of 

 Millam Park, and range towards the sea along that ridge with a 

 more regular strike, and a dip towards the south-east. Commencing 

 among the shattered masses of slate and porphyry above noticed, and 

 on the west side of the Greystone House fault (which runs nearly 

 north and south), there runs a second enormous fault south-east 

 and north-west down the Whitchamp valley as far as the sea-coast. 

 On the north side of this second fault rises the contorted Skiddaw 

 slate of Black Coomb f, which contains mineral veins (with lead, co- 

 balt, &c.), is pierced by dykes of quartziferous porphyry, and at its 

 northern end is altered by and jammed against the granite of Bootle. 

 Close to the junction the altered Skiddaw slate is pierced with fine 

 veins of true granite, rivalling some of the corresponding phaenomcna 

 of Cornwall. The upheaval of the system of Black Coomb produced 

 therefore, first, the great Whitchamp fault ; and secondly, not being 

 powerful enough to break through the superincumbent slates and 

 porphyries farther to the north-east, shattered a portion of them to 



* This enormous fault, produced by an upcast to the south, has been described 

 in my former papers, and is laid down on the coloured county map in the possession 

 of the Geological Society. 



t See the annexed diagram, in which the rocks intersecting the slates (i) are 

 of this porphyry. 



