Vol. 57.] THE PASSAGE OF COAL INTO DOLOMITE. 297 



22. On the Passage of a Seam o/Coal into a Seam 0/ Dolomite. 

 By Atibkey Strahan, Esq., M.A., F.G.S.^ (Read June 5th, 1901.) 



[Plate XII.] 



In the spring of the year 1900 I was informed by Mr. N. R. Griffith 

 that the Seven-Peet Seam of the Wirral Colliery had been found to 

 pass into stone of an unusual character. The matter seeming 

 likely to be of scientific as well as of economic importance I received 

 instructions from Sir Archibald Geikie, then Director-General of the 

 Geological Survey, to visit the colliery and collect the facts. This 

 I did in June, under the guidance of Mr. James Piatt, the Manager, 

 to whom I am indebted for the information concerning the working 

 contained in the present paper. 



Pour workable coal-seams occur in this small Parkgate Coalfield, 

 namely in descending order, the Six-Peet, Pive-Peet, Seven-Peet, 

 and Two-Peet. Though they cannot be precisely correlated with 

 the seams either in Plintshire or South Lancashire, they almost 

 certainly belong to the Middle Coal-Measures. The Seven-Peet 

 Seam, with which alone we are now concerned, was reached at a 

 depth of 148 yards in jN^o. 1 Shaft, and the workings in it were carried 

 westward under the estuary of the Dee for more than half a mile, 

 as shewn in the accompanying plan (fig. 2, p. 299). Por a distance 

 of about 1600 yards from the shaft the coal was good and about 

 4 feet thick. A fault with an easterly downthrow of 23 yards was 

 then encountered (fig. 1, p. 298), but the coal was regained by driving 

 upward through the measures, and was found to be still fairly good. 

 A few yards farther on, however, bands of stone from 1 to 10 

 inches thick made their appearance in it, some of them consisting, 

 in Mr. Piatt's words, of spherical pellets like gunshot. Gradually 

 increasing in thickness at the expense of the intervening bands of 

 coal, these stone-hands eventually constituted the whole seam, the 

 last traces of workable coal disappearing at a distance of 250 yards 

 from the point where the change first began. The slant was 

 continued for 56 yards farther, in the hope that the coal would come 

 in again, but it proved only a continuous band of stone, 3 feet 

 thick. 



The roof and floor of the seam continued unchanged over the 

 barren area, hut a boring put up through the measures above the 

 coal proved that the overlying rock, which is usually white, was 

 very red and quite thick. The following account of the borings 

 is furnished by Mr. Piatt : — 



^ Communicated by permission ol' the Director of H.M. Geological .Survey. 



