340 GEOLOGY OF THE BEISTOL COAL-FIELD. 



Thirty-six seams of Coal are worked in the lower Coal measures. 

 Westward of Cromhall the beds are entirely covered over by the 

 new red. Here the upper Coal seam is 411 feet from the surface. 

 At Kingswood the seams are very irregular from numerous faults 

 and often rolled. In making the tunnel under the Severn the beds 

 of shale and coal were found to be frequently upheaved from these 

 undulations. At Bedminster and Ashton the seams come com- 

 paratively close to the surface. At Bedminster the first Coal seam 

 is reached at 174 feet, and at Ashton at 270 feet. The 

 Gloucestershire Coal-basin terminates here, being separated by an 

 anticlinal limestone ridge, from a smaller basin at ]S"ailsea. The 

 probable thickness of the JS"ailsea Coal measures is about 1350 

 feet. The Coal unfortunately is very poor and sulphureous, and this, 

 with an enormous influx of water, will, it is feared, stop any Coal 

 mining in this basin. 



South of the Mendip range, coal has been found, but the seams 

 appear to have suffered from the violent disturbance which raised 

 those hills and are ** faulted " to a very large extent. Many of 

 the seams give off fire damp. It is particularly troublesome at the 

 Edford collieries. Here the disturbance has been so great, that the 

 seams are nearly vertical. This is so at the Barton colleries also. 



Mr. Anstie thinks, with great probability, that these now 

 separate coal-fields were once continuous. 



When the shaft at Portskewet for the tunnel was made, several 

 thin seams of Coal from the lower measures were passed with very 

 hard firestone. The coal was full of fragments of ferns. 



As a rule, the Lower Coal Measures furnish a short list of plants 

 whose names have been determined, but, probably, this entirely 

 arises from want of a proper examination. Those that have been 

 identified as having found in the lower seams, are so marked in the 

 list of fossils at the end of this section. 



Pennant Sandstone. 



Upon the last of the Lower Coal Measure series, lies a mass of 

 sandstone rocks 1725 feet thick. The Pennant grit is peculiar to 



