A MODERN STREET. 215 



of great power, which renders the resulting block as solid as the materi- 

 als can be made. The Mocks are required by the specifications to be 

 -1 x 5 x 12 inches and to vary not more than one quarter of an inch in 

 dimensions. They are laid on their edges on a cushion of two inches of 

 sand, so that the surface presented to wear shall be 4 x 12 inches, either 

 in parallel rows or in a diagonal across the street. The surface, after 

 the wear of a summer, during the heat of which it softens slightly, be- 

 comes nearly coherent and as continuous as sheet asphalt. On grades, 

 the slight irregularities due to jointing offer a better foothold to the 

 hoofs of horses than sheet asphalt and in this respect the asphalt blocks 

 are the best. It is found in practice that on streets subjected to very 

 heavy traffic, asphalt blocks are more easily broken than a good quality 

 of sheet asphalt, but for streets that are subjected only to light traffic, 

 asphalt block pavements are durable, clean and sightly, and cost little 

 or nothing for repairs over long periods of time. 



The larger number of so-called asphalt streets are laid with sheet 

 asphalt, in imitation of the surface first laid about fifty years ago in 

 France from the natural bituminous rock occurring at Pyrimont and 

 Seyssel, near the border of France and Switzerland and near the head- 

 waters of the river Rhone. This material consists of chalk saturated 

 with bitumen, which, when extracted, is found to be very permanent in 

 the air, impervious to water and very tenaciotts. When the bituminous 

 rock is heated to a moderate temperature it falls into powder that can be 

 screened to remove the flints that are in the chalk. It is then spread, 

 while hot, with rakes, and rolled into a sheet that lasts until it wears out. 

 This bituminous rock was called 'asphalt' by M. Leon Malo, the dis- 

 tinguished French engineer, through whose efforts and inventive skill 

 the laying of these streets became an established industry in France. 



M. Malo did not identify 'asphalte' as thus named by him, with 

 asphaltum, which is the solid variety of bitumen, and had been known 

 for an immemorial period before any one thought of using bituminous 

 limestone in the construction of streets. 



M. Malo says in his paper, published in 1861 : 



Tlie first point is to establish the value of the definitions and of the 

 words. ' 



To this end he proposes a nomenclature of which he gives the fol- 

 lowing summary: 



First, bitumen or pitch, the materials which impregnate asphalte. 

 Second, asphalt, the calcareous rock, impregnated naturally by bitumen or 

 pitch. 



This definition gave this peculiar bituminous mineral a name that 

 passed to the streets made from it, and these streets became known in 

 England and the United States as "asphalt streets.' 



