ASPHALTUM FOR A MODERN STREET. 



229 



Koch. This pavement was formed of fragments of quartz and of mastic 

 of coal-tar, upon a bed of sandstone, the joints of which were filled with 

 the mastic. These coal-tar streets, even with a concrete base, were 

 not satisfactory, thus early establishing the undesirable qualities of coal- 

 tar preparations in the construction of streets. 



He states his preference for the asphaltes found at Seyssel, Val de 

 Travers and Lobsan, which are composed principally of carbonate of 

 lime and bitumen or sandstone and bitumen. As found in nature, these 

 asphaltes consist either of chalk, sandstone or coarser gravel which 

 have been filled to saturation with bitumen, which when extracted or 

 separated from the mineral constituents of the rocks, is semi-fluid, re- 

 sembling mineral tar. The deposits occur in beds between more dense 

 and barren rock, and are mined out by running galleries and tunnels 



Fig. 2. Digging and Removing Pitch from the Lake prior to 1890. 



into the hills that border the valleys, in a manner similar to the mining 

 of coal in some sections of country. 



Other deposits of similar material occur at Eagussa, in Sicily, and 

 at Limmer, in Hanover. The Seyssel and Neufchatel rocks are gen- 

 erally preferred for streets, as they contain more lime and less sand, and 

 are also freer from sulphur compounds. 



On the North American continent there are deposits of vast extent 

 both of asphaltum and asphaltes. Generally speaking, asphaltum is not 

 used in street construction; the deposits being either too pure, and hence 

 too valuable for such uses, or, on the other hand, so impure as to be 

 purified only at too great cost. As the asphalte is used in enormous 

 quantities, freight becomes a very important consideration in the selec- 

 tion of the material used in any given locality. This item of cost has given 



