Page:Popular Science Monthly Volume 81.djvu/178

172

The general surface of the lake is very irregular and hard. There are many very narrow and irregular channels or depressions from a few inches to four feet deep, filled with water, and, not being easily distinguished, one often falls into them. At the foot of the growth of grass and shrubs are ridges of pitch mingled with soil and decayed vegetation, which have been plainly coked and hardened by fires originating in the surface growth. When this hardened material which forms only a crust is removed, asphalt of a kind suitable for paving is found. The crust is from a foot and a half to two feet in depth and very firm, while the asphalt underneath would not begin to sustain the weight which that of the Trinidad pitch lake does easily. There are breaks in the crust here and there through which soft pitch exudes, as has been described.

It appears, therefore, that the Bermudez deposit owes its existence to the exudation of a large quantity of soft maltha, which is still going on and which has spread over a great area; that this has hardened spontaneously in the sun, and has also, by the action of fire, been converted over almost the entire surface into a cokey crust of some depth, beneath which the best material lies, and that here and there are scattered masses of glance pitch produced in a similar way from the less violent action of heat. There is no evidence of a general movement and mingling of the mass of this deposit in any way that would produce a uniformity of composition, as seen in the Trinidad pitch lake, although there is a certain amount of gas evolved at the soft spots where maltha