Page:Popular Science Monthly Volume 58.djvu/239

Rh has its source in subterranean springs. The areas of pitch arc of considerable extent, highest in the middle, but still nearly level and gently sloping on all sides to the precipitous edges of the water areas. These areas are being continually elevated in the center by rising gas, which, forcing up the center in huge bubbles, cause a continual ebullition of the plastic mass and a gradual transference of the material from the center towards the circumference, so that trunks and branches of trees submerged in the pitch come to the surface, rise, and after assuming a perpendicular position, are in time again submerged to an unknown depth. From the escaping gas the whole central portion of the lake is maintained in a constant motion that prevents vegetation

from taking root, and leaves the surface of the areas of pitch bare and of a blue-black color.

When the pitch is dug, a negro will drive a long, slender pick to the eye at a single blow, and, by using the handle as a lever, will break out a flake of pitch larger than he can lift. From less than an inch below the surface the pitch is of a brown color, saturated with water and filled with bubbles of gas. A broken mass will soon dry on the surface and melt, forming a pellicle that will enclose the wet mass for years and prevent the escape of the water. In this wet and porous condition it is called 'cheese pitch.' It is not sticky at all, as the water can be squeezed from it in the hand, as if it were a sponge.

Formerly the large lumps of this cheese pitch, as it was broken out, were transported to the beach in carts, but about 1893-4 a wharf was