C— GEOLOGY. 67 



the coal over an area of some hundreds of acres. The sandstone is a 

 strongly current-bedded rock GC> to 8U feet in thickness. Bands of 

 conglomerate, including at times masses of 2 or 3 feet in length, occur. 

 The smaller stones consist of clay ironstone concretions, sometimes with 

 their original form but littk' modified by attrition. The larger blocks 

 are mostly of sandy shale. Eipple markings are frequent, and large 

 limbs or trunks of trees are encountered. The whole aspect presents a 

 very close resemblance to sections of the old bed of the Eiver Irwell 

 exposed in the cuttings for the Manchester Ship Canal. 



This channel must evidently have been that of a river of considerable 

 size which commenced to erode on a plane far above that of the Park- 

 gate seam. This is indicated, not merely by the thickness of the mass, 

 and by the evidence afforded by the pebbles and larger blocks of the 

 erosion of Coal Measure materials, but also it will be noted that the 

 pebbles are chiefly of clay ironstone, betokening a lapse of time sufficient, 

 not only for the deposition of shales, but for the formation of ii'onstone 

 concretions. This need not, however, have been a very protracted 

 period. The Pleistocene Leda clays of Ottawa contain concretions quite 

 comparable with those now under consideration. 



The form of this river channel cannot, at Aldwarke and Eotherham 

 Main, be defined, for the interposition of a few yards of shale would 

 remove it from the ken of the miner except whei'e shafts, or cross- 

 measure drifts to traverse faults, explored the rocks more thoroughly, 

 but it is evident from the records of neighbouring collieries that the 

 Parkgate Eock is not one of the widely extended sandstones of which 

 examples occur in this coalfield, and we may therefore regard the 

 channel which it fills as of limited breadth. 



Another instance of the same kind in a seam about 650 feet higher 

 in tlie Coal Measure series is furnished by the Haigh Moor Eock. which 

 in some places encroaches upon the Haigh Moor Coal seam. It rests 

 upon a conglomerate composed of clay ironstone nodules which, in this 

 instance, can be traced with much probability to their source, for at 

 Eobin Hood, about midway between Leeds and Wakefield — where the 

 whole series of strata adjacent to the Haigh Moor seam is exposed in 

 a great excavation, affording one of the best sections of Coal Measures 

 in Yorkshire — the seam is surmounted by a varied suite of rocks com- 

 prising coal-seams with their underclays, thin beds of sandstone, and 

 shales containing great numbers of clay ironstone nodules. Such a 

 suite would yield the constituents of the Haigh Moor Eock. 



Though it is not practicable to define the course of this rock-filled 

 channel in the way that has been done for the great Warrensburg 

 channel of the Missouri Coalfield, there is yet a convincing proof that 

 it is not an example of folding and denudation, for, if that were the 

 case, the strata would show a diminution as measured from seam to 

 seam as the area is approached, but the area occupied by the rock is 

 just that where the great thickening takes place alluded to a propos the 

 splitting of the Barnsley Bed. 



An inference of some moment can be drawn from these two eroded 

 channels — general subsidence of the Coal Measure area must have been 

 interrupted at least twice by actual elevation or we should not find 



