226 CORNISH VIADUCTS. 



were therefore cramped inside their own fences, and adopted 

 the expedient of building the viaduct in two halves, divert- 

 ing the line to the one half whilst they pulled down the old 

 viaduct and built up the other. The piers were spaced so as 

 not to interfere with the existing ones, thus enabling the 

 whole of the concrete foundations to be laid at one time. 

 Strips of hoop iron were left projecting all the way up the 

 unfinished sides of the piers and abutments, and built into 

 the second half in order to assist in bonding the two 

 thoroughly together. This they seem to have done ; for 

 no unequal settlement of the two halves appears to have 

 taken place, the whole viaduct being perfectly homogeneous, 

 as if it had all been built up together. 



Since Bolitho is one of the standard pattern viaducts, it 

 may be well to detail in order the works in connection with 

 its construction, and this explanation will apply to all the 

 later viaducts. 



The survey having been made, and the drawings prepared 

 and approved, the extra land, if necessary, is negotiated for. 

 The new centre line of railway is then ranged out, and the 

 bases of the piers and abutments marked out for excavation. 

 When the concrete is set, the centre line is again picked up, 

 and the quoins of each pier, or abutment, as the case may 

 be, are carefully set out with steel tape and theodolite, the 

 four first quoin stones being set upon the spot, whilst the 

 engineer is present. 



The masonry, which is then carried up, is left with a rough 

 rock face in "random range work." The error in batter is 

 allowed for, as already explained, and the pier is carried up 

 to springing by the derricks. Here the following method 

 is adopted for supporting the centres. Wrought iron bands 

 are built into the pier, with their thin end downwards, pro- 

 jecting a few feet on each side. Ordinary wooden brackets 



