THE SEVERN TUNNEL. 



6? 



rim tliroiigli a first time and the points marked, tlio tele- 

 scope was turned over in its Y's, and the whole line sot out 

 a second time to see if there was any instrumental error. It 

 was then found that there was a slight instrumental error, 

 for the two lines gradually diverged' in a very flat curve, and 

 wore nearly two feet apart at the end of a mile — tlie true 

 centre line was consequently just half-way between the two, 

 and thus the permanent centres were fixed. 



The heading was then carried forward under the Shoots, 

 where the Pennant was of a grey colour, and so hard and 

 close that no joints were visible, until the Shoots had been 

 passed. The heading then began to I'ise again, according to 

 the gradient, and after a time emerged from the top of the 

 Pennant into the upper coal shales, where it passed through 

 two beds of coal, ten and twelve inches thick, until it came 

 to a vertical fault, 2,180 yai'ds from the shaft, where it 

 suddenly entered the new red sandstone. This rock was 

 verj hard to drill (machine drills were used, driven by com- 

 pressed air), n,nd when blasted, the dynamite only blew out 

 a round hole ; but blew the sandstone into powder. This 

 powder was of a singular nature : after it had been filled into 

 the iron trolleys, in passing along the heading it got shaken 

 down so tightly that all the water was driven to the sur- 

 face, and tlie sandy mateiial below was wedged in so fast 

 that when the trolley was run to the tip it would not come 

 out, but carried the trolley with it, rolling over and over 

 down to the bottom, where it was found tight in the trolley 

 still ; so that the men had afterwards to set the trolley up 

 on ond, find get the stufl^ out with a pickaxe. The writer 

 never met with any material like this before, except in 

 " Kellaways Sand," in Wiltshire. If you there dug a hole 

 in the ground, the stuff that came out would not fill the hole 

 again. A man of his there had to fix a big gate-post, and 



