PKOCEEDINGS OE GEOLOGICAL SOCIETIES. 



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there is another coal, called the "bassey mine," lying abont 30 yards 

 above it. 



At Birchinley, near Rochdale, the coals still retain the same names, and 

 also at Dearnley and Cleggswood. Passing on through Whitworth and 

 Wardle to Bacup, the 40-yards mine takes the name of the little or top, or 

 half-yard mine. At Whitworth, Wardle, etc., portions of the Gannister 

 coal, where it originally cropped ont all round some of the hills, have been 

 entirely worked out, and small workings are commenced on the lower foot- 

 mine. The Gannister coal at Bacup is called the yard, or main coal ; the 

 lower foot and the sand-rock mines still retaining their names. 



Up to this point there is no difficulty whatever in following the order in 

 which these coals lie. The strata follow each other with surprising regu- 

 larity, seldom varying more than 10 yards in thickness between the same 

 coal-seams. 



About a mile and a half to the north-east of Bacup one of the large faults 

 passes in a north-westerly direction, causing some alteration, and at the 

 opposite side of that the principal coal of the Gannister series is known at 

 Cliviger and all round the northern part to Colne as the " mountain four 

 feet," and it is there generally accompanied by an unusually large number 

 of very fine specimens of Goniatites and other fossil remains. 



Returning to the south-west side of the large fault, between Bacup and 

 Cliviger, the Gannister coal, which was at Bacup 4 feet thick, becomes much 

 thinner in a westerly direction. 



At Over Darwen the Gannister coal is called the "lower," "70 yards," or 

 " half-yard " bed. The principal seam above it is there known as the " yard 

 coal," which, together with the " little coal " above it, corresponds with the 

 " 40-yards " seam. The flag and tile-rock of Darwen lies about 40 yards 

 above the "yard coal." The strata, about 10 yards in thickness, which se- 

 parate the "little coal" from the " yard coal," at Darwen, gradually thin out 

 in the direction of Hoddlesclen. Ac the old Hoddlesden Colliery the two 

 seams were found gradually approaching each other until they came so near 

 as to be worked together ; and now, where they are being worked, there is 

 only a division of black earth between, the rock being entirely nipped out. 

 They continue together as one seam for some distance, but ultimately they 

 divide out again, and at Belthorn the upper part is called the " half-yard," 

 and the lower the "little coal." At Brookside and Duckworth Hall they 

 again lie together, and are called the " Poor Robin " bed. At Chorley, and 

 also at Heath Charnock, the corresponding coals are known as the "little" 

 and the " higher mountain." At many of those places this "little" coal has 

 a rock floor, which has often been mistaken for the true Gannister. 



The total thickness of the strata between the Gannister coal and the 

 Arley mine is, at Oldham, about 300 yards. At Simpson Clough it seems 

 to be thinner than at any other point, being only about 253 yards. At 

 Clayton, the distance is about 308 yards from the Arley to the Gannister. 

 Adding to this the total thickness of strata in which coal-seams are found 

 below the Gannister, namely, 326 yards, as shown at Mossley and Harts- 

 head, gives a total thickness of about 625 yards of coal-bearing strata in 

 the lower or Gannister series alone. 



The middle series, from the Arley mine to the "Worsley four- feet, is about 

 975 yards in thickness. The upper series, above the Worsley four-feet, 

 has been proved at Patri croft to a thickness of 390 yards, but this is not 

 the whole of it, and including the measures at Clayton, near Manchester, 

 it is about 550 yards in thickness. The total thickness of coal-measures 

 in the upper, middle, and lower series, to the lowest coal-seam, is therefore 

 about 2150 yards, exclusive of the grits and limestone shales below. 



