THE SEVERN TUNNEL SECTION. 



87 



the white Sandstone was close and hard, and an excellent 

 building stone. 



We know fi'om the Aust Cliff section that tlio Kenper 

 beds are there 114 feet thick. This is all we have in tlie 

 Severn Valley to represent the 3,500 feet of Keuper in 

 Cheshire. The Bunter, more than 1,000 feet thick in Cheshire, 

 is wanting. The Permian beds are also wholly absent. In 

 this district, therefore, after the npheaval of the Palosozoic 

 formations, there followed a prolonged period of continental 

 conditions and consequent denudation. During this period 

 many of the sculptured features of Severn scenery were 

 produced. These were subsequently buried beneath 

 niesozoio strata, and it has been the work of post-mesozoic 

 denudation to remove the secondary wrappings around this 

 ancient sculptured surface. 



3. Palmoeoio liochs. — During the construction of the 

 Bristol and South Wales Union Railway, the great Catty- 

 brook fault was discovered. This brings Coal Measures 

 against Upper Limestone Shales. Farther down the river, 

 at Porfcishead, a great fault brings Pennant against Old Red 

 Sandstone. Such faults, which may have had much to do 

 with the determination of the line of the Severn Valley, 

 prepared geologists for the existence of strata of Coal 

 Measure age beneath the Severn. Tlie section shows how 

 these beds have been proved in the Severn Tunnel. It also 

 shows the occurrence of minor faults. 



Concerning the Pahnozoic rocks, Mr. Rvtm D. Jones, 

 sometime assistant engineer to the Severn Tunnel works, 

 has contributed valuable information to the Proceedings of 

 the Oeologids Association, vol. vii. From him I quote :— 



"The Coal Measures were entered under the Triassic 

 Conglomerate, and the information on this point afforded 

 by the excavations for the Severn Tunnel, is that to which 



