88 



THE SEVERN TUNNEL SECTION. 



the greatest interest attaches. The Pennant Grit, passed 

 through und(!r the Conglomei'ate in this shaft, had a 

 vertical thickness of 19 feet, dipping towards tlio centre of 

 the river, or a few degrees S. of E., at about 1 to 12, its upper 

 surface here forming the plain of denudation upon which 

 the Trias has been deposited. Beneath the Grit were 35 

 feet of the Lower Coal Measures, dipping in the same direc- 

 tion, 2^) feet consisting of Clay Shales, and 10 feet of Coal 

 Shales, separated by a 2-inch seam of coal. These rested 

 on Millstone Grit, 11 feet thick, under which were intoT'- 

 niinglcd beds of Firestone and Shale, about 6 feet thick 

 Under the Shale came a remarkable bod made up of Inmps 

 of Mountain Limestone, with angular corners, embedded in 

 the Shale, 14 feet in thickness ; the lumps varied in size 

 from small pieces to blocks as lai'ge as a wheelbarrow. The 

 remaining 2G foot of the shaft penetrated a very hard, close- 

 grained, red fircstono, or ii'onstone (as it was called by the 

 miners), occurring in regular beds from 6 to 12 inches 

 thick, separated by layers of hard fire-clay about an incli in 

 thickness. 



" From this shaft two headings have been driven under 

 the river, a lower one commencing at the bottom of the 

 shaft, and an upper one 40 foot from the bottom, the former 

 being continuous, and nearly two miles long. 



" The upper heading begins in the Millstone Grit, and the 

 floor of the heading continues in it for 50 yards, but the 

 roof passes into the Coal Shales at a distance of 10 yards. 

 The length of Coal Shales passed through was 20 yards, and 

 it was followed by the Shales for a length of 110 yards, 

 when the Pennant was entered. 



"In the lower heading the same kind of rock that oc- 

 curred at the bottom of the shaft was found for a distance 

 of 40 yards, when the limestone blocks in shale were reached. 



