402 Institution of Civil Engineers. 



the tunnels are 30 feet in height from the line of rails, and 30 feet 

 in width ; they are curved to a radius of about 1 20 chains ; the 

 gradient of that part of the line is four feet per mile. The strata 

 through which they were driven consisted generally of hard gray 

 sandstone and shale, with the gray and dun shiver, &c. ; in a few 

 places only, the new red sandstone and red marl were traversed. 

 Every precaution was taken for securing the roofs, by lining them 

 with masonry where the nature] of the strata demanded it, and in 

 some places invert arches were turned beneath. 



Driftways were driven before the tunnels were commenced, and 

 shafts were sunk to enable the work to proceed at several points 

 simultaneously. The modes of conducting the works by these means 

 are fully described, with all the difficulties that were encountered. 

 The construction of the centres is given, with the manner of lining 

 the arches with masonry, which is stated to be what was termed 

 " coursed rubble;" but was of a very superior description, and in 

 every respect similar to ashlar- work. 



The author offers some remarks with regard to the expense of 

 working tunnels by means of centre driftways. He states this plan 

 to be costly, and in many instances without corresponding advan- 

 tages, on account of the difficulty of keeping the road clear for the 

 waggons. He recommends that when driftways are used they should 

 be on the lower side of the dip of the strata, as the excavation would 

 be facilitated, and the road would be kept clearer. In long tunnels 

 he has found the cheapest and most expeditious mode of working 

 to be by excavating the centre part from shafts, and both the ends 

 (together if possible) from the extremities after the open cuttings 

 are made. The drawing accompanying the paper gave a longitu- 

 dinal section of all the tunnels, and showed to an enlarged scale 

 several transverse sections of them, where the variations of the strata 

 rendered either partial or entire lining necessary. 



In answer to questions from Mr. Vignoles and other members, 

 Mr. Nixon explained that the extra number of shafts had been re- 

 quired in order to enable the works to be completed within a given 

 time : there had not been any accidents during his superintendence, 

 but subsequently one of the shafts had collapsed. The cost of 

 driving the driftways, the dimensions of which were 7 feet wide by 

 8 feet high, was ten guineas per yard lineal. He then described 

 more fully his proposed plan of cutting the driftways on the lower 

 side, instead of the centre of the tunnel, and stated the advantages 

 chiefly to consist of a saving in labour and gunpowder, as a small 

 charge sufficed to lift a considerable mass of rock when acting from 

 the dip : the road was also less liable to be closed by the materials 

 falling into it when the enlarged excavation proceeded from one side 

 instead of upon both sides. 



Dr. Buckland, after returning thanks for his election as an hono- 

 rary member of the Institution, expressed his gratification at the 

 prospect of a more intimate union between engineering and geology, 

 which could not fail to be mutually beneficial, and cited examples 

 of this useful oo-operation in the cases of railway sections, and 



