MODERN STREET-PAVEMENTS. 85 



little more than three years in wood pavements, nearly all treated ; 

 many of them are now in an advanced state of decay, and, from the 

 degree of preservation after two or three years' use on suburban 

 streets with hardly any wear, one cannot approve of any of the pro- 

 cesses applied, since none of them have effectively neutralized the 

 destructive local agencies, or made up for inferiority in the quality of 

 lumber used. Square, polygonal, wedge-shaped, and undressed round 

 blocks, of pine, spruce, and juniper wood, set in rows, interlocking or 

 parted by interstices, upon sand, board, or concrete foundations, were 

 tried, so that all classes of patentees had chances to trot out their 

 hobbies and gratify their passion to serve the community. Though 

 this is an interesting study, we cannot in this place do full justice by 

 entering into details. 



The idea of ranking expensive wood pavements, treated and un- 

 treated, as valuable standard pavements, where more substantial ma- 

 terials can be procured at the same or lower prices, will, before 

 long, hardly more than elicit a smile from the critical expert. 



In this state of the problem, it may be considered as a new epoch 

 in city-life that the increased facilities of commercial intercourse, by 

 cheapening the cost of transportation, liave brought a relief within 

 reach, namely, asphaltum for roadways. The nature of asphaltum is 

 frequently misunderstood, because the mineralogist, in speaking of 

 asphaltum, has reference to the brittle bitumen usually found in Na- 

 ture, while the civil-engineer designates by mineral asphaltum a po- 

 rous limestone, in combination with tough bitumen. This limestone 

 was primarily impregnated by volcanic action with petroleum, which 

 appears to have oxidized within the structure of the stone by the 

 slow action of many centuries. Thus both ingredients have been 

 united so thoroughly in the asphaltum that neither heat nor water, 

 nor the combined action of both, in causing decay, can render it hard 

 and brittle by abstracting the tough bitumen from the limestone. It 

 is not strange that the efforts artificially to imitate this intimate 

 union have often produced materials witli quite different powers of 

 resistance against the various destructive agencies and vicissitudes of 

 climates ; and that the lack of durability not to speak of numerous 

 dead failures in various compounds of raw or treated coal-tar and 

 coal-pitch with coal-ashes, saw-dust, cinders, sand, gravel, etc., com- 

 monly called concrete pavements, which have reduced moderately 

 dii'ty streets, under the influence of the heat of summer, to vast sticky 

 quagmires has formed a serious drawback to the introduction of bet- 

 ter material, and especially the well-tested native asphaltum, which 

 will probably, in our climate, many times outlast the best artificial 

 composition yet known, as it has done in other countries. The 

 admixtures and distillations from coal-tar and pitch have been amply 

 relied upon as the base for artificial concrete, on account of a sup- 

 posed resemblance to the native asphaltum. This idea, however, is 



