Page:Popular Science Monthly Volume 81.djvu/39

Rh

In what has been said hitherto reference was had to the asphalt taken from the lake deposit itself. As has been mentioned, there are deposits of bitumen between the lake and the sea, and the material taken therefrom is known as land pitch. It has been subject to atmospheric weathering and by contact with the soil for years, as a result of which its physical properties are inferior to those possessed by the lake deposit. The greater the distance from the lake at which the land pitch is found, the more it shows signs of age and weathering and the more inferior it is.

There has recently been developed on the Island of Trinidad, in the neighborhood of the pitch lake, a new source of binding or cementing material of a very desirable character for surface application to roads, and for the productions of a residual pitch of a high grade. It has been called a liquid asphalt, and must have been the source of the asphalt found in the main deposit, and of the material which now forms the soft spot in the middle of the lake. It was recognized in the earliest days of the Trinidad asphalt industry that the millions of tons of asphalt existing in the old crater must be associated with some mother