TUB SEVERN TUNNEL SECTION. 



89 



The limestone was hero continued for 90 yards, occnrrin<>- 

 first in strips about throe feet thick (of wliich tlioro were 

 six interlaminated with shales), but becoming more massive 

 towards the end, where a block about 12 yards thick at the 

 bottom and tapering away to a point at the top was met 

 with, which appeared to be but a projection of the limestone 

 underneath into the overlying shales. 



" The next 40 yards were in the bed of shale which was 

 found under the Millstone Grit in the shaft, and were fol- 

 lowed by 40 yards of Millstone Grit, 30 yards of Coal Shales, 

 and 70 yards of Clay Shales, the two latter representing the 

 Lower Coal Measures. Resting upon these, the Pennant 

 was again entered. It extended in one solid mass (with the 

 exception of a few beds of interlaminated clay shales) for 

 nearly a mile, carrying the heading about 500 yards beyond 

 the Shoots channel. A considerable quantity of water was 

 met with in various places in driving through it, about 150,000 

 gallons an hour altogether. The Upper Coal Measures were 

 next entered, and were found to consist mainly of hard Clay 

 Shales. In the portion immediately overlying the Pennant 

 two seams of good hard coal were struck, one 15 inches and 

 the other 10 inches in thickness. Some thin beds of Pennant 

 were also found in this shale. The heading continued in 

 these Upper Coal Measures for about 400 yards, when a 

 sudden change took place, and the New lied Sandstone, 

 which is here faulted down against the Coal Measures, was 

 entered. 



" Appended is a tabular list of the strata passed through 

 in Shafts No. 3 and 4, and the heading from the latter 

 driven last, which are the most important parts of the work 

 geologically considered : — • 



