220 CORNISH VIADUCTS. 



by a high embankment, and the other by a retaining wall 

 and bank. Ten have been replaced by masonry arched via- 

 ducts, and two, St. Pinnock and Largin, in the Glynn Valley, 

 by iron girders with masonry piers. The total length of 

 wooden viaducts thus renewed now amounts to about 1'2 

 miles. On the West Cornwall Line, out of ten viaducts 

 seven have been rebuilt in stone and iron. All of these are 

 built to eventually accommodate a line of double narrow 

 gauge. 



As a rule the masonry viaducts differ but little from one 

 another. Now that nearly all the higher ones have been 

 rebuilt, there is little cause for any distinct departure, and 

 a standard pattern has consequently been adopted, which is 

 preferable, not only on account of the labour saved in calcu- 

 lation, but also because of the immense reduction in the cost 

 of centering, etc. 



The standard arch, of which thirty- three are being or 

 have been built upon five viaducts, averaging 90 feet mean 

 height, has a span of 56'7 feet by 20 feet rise, the radius of 

 intrados being 30 feet. 



The piers have a batter of about 1 in 50, and are built of 

 Westwood slate stone and quoins of granite, upon concrete 

 bases. The arches vary in thickness from springing to 

 crown, and also from face to centre of viaduct, the voussoirs, 

 which are of granite, being thinner than the rubble backing 

 behind. Jack arches fill the spandrils, and together with 

 the arch are covered with a good coat of asphalte before the 

 ballast is laid. The parapets are very plain, and have open 

 spaces, protected by iron bars, left at intervals to act as 

 manholes. With the exception of one or two of the earlier 

 ones, all the reconstructed viaducts on the Cornwall Railway 

 have been carried out by the Company themselves. This 

 course was adopted in preference to the usual one of employ- 



