ly, was paid to the construction of roadways. Cobble-stones were resorted to for paving-purposes, since they were easily obtainable in the alluvial plains in which most modern cities are founded. They were succeeded by irregular quarried stones of such quality as was within easy reach; then by larger square blocks, mainly of trap-rock or granite, such as were thought necessary in streets with heavy traffic. But experience has proved that the jarring against them compelled the construction of heavier wagons, and that their peculiar smoothness by wear caused the horses to fall, and so this material was modified to uniform oblong blocks in narrow courses. These, after severe tests, have maintained a truer surface, have been found to offer a greater resistance against wear, to lessen the noise, and to decrease considerably the number of accidents to horses. They are called, in common with the former, Belgian blocks.
A most important sanitary feature, almost entirely neglected before the rapid concentration of population in the cities, now demanded attention. The cubical stone blocks are displaced under the prodigious traffic, the corners and edges are worn away, the surface gets to be irregular, the joints are widened. The filth of the streets gathers in ruts and joints, is recruited constantly by new accessions of urine, horse-dung, and silt, and, diluted by the rain, it ferments, and forms a putrescent organic mire, becoming in course of time a source of noxious miasmas. In hot and dry weather these nauseating deposits pass into the atmosphere in the form of unhealthy vapors, or, pulverized and drifted by the wind, cause inconvenience and poison our lungs. Indeed, in repairing old pavements, a black layer of ground, saturated with sulphuretted hydrogen, is found below the stone blocks, and bears witness to the infection of the subsoil by the soakage of contaminated water. Prof. Tyndall has established by experiments that a large proportion of the particles of dust in the rooms of London houses is of organic origin, and other experiments have demonstrated that horse-manure, in a state of decomposition, is a permanent ingredient.
Vapors still more noxious than those from the road-bed of the streets rise from the gutters, the subsoil of which is saturated to a considerable depth by more concentrated matter of the described composition, and also from the surface of alleys on which are the houses of great numbers of people of limited means. Crowds of dirty children, whose tender lungs breathe the air immediately over this miasmatic soil, here contract constitutional predispositions, which doom them to a languishing and miserable life, and render them an easy prey to epidemics. This infection of the subsoil has been prevented, with a certain degree of success, by foundations of concrete. There is still another feature of stone pavements in the heart of cities, which affects the inner man more than the physical frame, viz., the rattling and noise, under heavy traffic, accompanied, in alluvial soil, by vibrations
