﻿344 wash-outs in the middle coal-measures. [may i905, 



The Paekgate Seam. 



In fig. 4 (pp. 342-43), the sections A, B, C, D, E, E, & G are 

 also taken from actual measurements, and their positions are denned 

 on the plan (fig. 1, p. 339). 



The average thickness of this seam is 4 feet 6 inches, as described 

 in fig. 4. In most cases the Parkgate Rock overlies the coal : 

 from these sections it will be clearly seen where the seam has been 

 removed. 



The material that has replaced the coal differs very slightly from 

 the ordinary rock overlying the coal, but sometimes a bind or argil- 

 laceous shale (which decomposes into a clayey soil on exposure to 

 the atmosphere) interposes between the rock-roof and the coal for 

 a few yards, at other times for 200 to 300 yards. In some cases, 

 this bind thickens to 4 or 5 yards. 



In sections C, D, and G (fig. 4), a conglomerate-rock interposes, 

 with pebbles ranging in size from about half an inch in diameter to 

 oval-shaped boulders 18 inches long. 



In conclusion, my opinion is that the wash-outs occupy the sites 

 of winding streams or rivers ; these, during the formation of the 

 coal-seams, meandered through the alluvial tracts in which the 

 seams were being laid down, and washed the vegetable matter 

 away, replacing it with sediment of a different character which the 

 streams held in suspension. 



Discussion. 



Mr. Pox Steangways said that these wash-outs were very 

 common in the Leicestershire and South Derbyshire Coalfield, but 

 there was one curious case on the western side of the Coalfield to 

 which he ventured to draw the attention of the Society. This 

 occurred in the Eureka seam of coal in the Netherseal Colliery, 

 and was pointed out to the speaker by Mr. G. J. Binns. In this 

 case the wash-out, instead of being one broad hollow, consisted of 

 numerous confluent streams, which united together into a main 

 channel like the head- waters of a drainage-system. It would, 

 therefore, appear that some wash-outs were caused by stream- 

 denudation after the formation of the coal-seam. 



Prof. P. F. Kendall pointed out the unusual interest attaching 

 to the superposition of two wash-outs, in seams separated by a 

 considerable interval. At Silverwood the depth to the Barnsley 

 Bed was 745 yards and at Cadeby 750 yards, and this was the 

 typical area of development of the Red Rock of Rotherham, inter- 

 preted by the late Prof. Green as a wash-out. There might be 

 some significance in the proximity of the pre-Permian Don-Valley 

 Eaults, and it was just possible that wash-outs were explicable on 

 the theory of contemporaneous movement. 



