654 PROCEEDINGS OF SECTION H. 



xeduced to about one-half at the sides ; over this foundation was spread 

 a coat of 2^in. metal to a depth of Tin. in the centre and somewhat 

 less at the sides. The bottohi course was carefully levelled, graded, 

 and compacted with small stones by hand to keep earth from working 

 up through road metal and ruining road, as might readily happen on 

 soft ground ; the top coat was covered with lin. of gravel. 



Telford's magnum opus was, however, the construction of the 

 Shrewsbury and Holyhead Road, one of the finest pieces of road en- 

 gineering carried out up to that time. The surface traversed consisted 

 of rocks, bogs, ravines, and precipices. In those days road pavements 

 were consolidated by the traffic, with all the attendant inconvenience, 

 losses, and delays. 



Since the advent of the steam road-roller the making of macadam 

 roads has entered a new phase. The formation is made parallel to the 

 finished surface, and instead of pitchers hand-packed, 4in. metal is 

 now laid for a bottom or foundation course where one is required, and 

 a. top course of 2in. or 2hin. metal lightly blinded and well rolled by a 

 steam roller weighing from 10 tons to 20 tons. Under the old system 

 it took months to consolidate a road, but nowadays they are made 

 to-day and are in use to-morrow. They may now be made any time 

 of the year, though the autumn is the best season, instead of only in 

 the winter as formerly, and they withstand heavier traffic. This is in 

 brief the recognised standard system on which the best macadam 

 Toads are now made. 



The rationale of the different pavements alluded to is as follows : — 

 The Roman pavement was made as solid as possible, partly owing to 

 difficulty of draining foundation, and partly to insure durability and 

 minimum of maintenance. With large flat stone foundation the top 

 €ourse of metal must be thick or the flat stones must be in several layers. 



A thick coat of metal distributes pressure and prevents a load being 

 'Concentrated on one particular part of flat stone. With a thin top 

 course and one layer of flat stones there is a local concentration of 

 load, and the flat stones will surely cockle and rock sooner or later, 

 letting rain into foundation and ultimately ruining the road. The 

 Romans therefore adopted two or three courses of flat stones, sometimes 

 cemented together. 



Where a road is formed below the natural surface, or where the 

 surface is bad, a strong foundation is advisable ; but before the advent 

 of the steam roller the only possible way to attain this end was by 

 laying hand-packed stones on flat with points upwards, wedged and 

 jammed with small stone shivers tightly driven in. This prevented 

 the soft earth working up and destroying the surface, and enabled the 

 great thickness of the Roman road to be halved and the expense re- 

 duced ; but drainage had to be carefully provided for. This was the 

 system of Tresaguet and Telford. 



Wherever the natural formation is good a lOin. coat of metal 

 broken to a 2in. gauge is sufficient to distribute the weight of a vehicle 

 with moderate load without injury to earth foundation ; and as, 

 without a heavy roller, all dirt, &c., that is put on to such road while 

 the metal is loose must stay there, it is preferable to use grit. Where 



