THE MUSEUM. 



207 



it is the product of land vegetation. 

 Indeed, under the proper conditions, 

 it would have become coal itself. The 

 most important of these conditions is, 

 perhaps, temperture; for it is a curious 

 fact that asphaltum is found chiefly in 

 warm countries, while coal occurs in 

 colder latitudes. 



Coal and petroleum are so wide- 

 spread and abundant in our own coun- 

 try, that the general conditions under 

 which they occur, and the usual modes 

 of obtaining them, are familiar to 

 every American student of geology; 

 but no adequate account of the great 

 tropical deposits of asphaltum can be 

 found even in the best general works 

 on geology; and the special object of 

 this article is to supply this deficiency 

 by a somewhat detailed description of 

 a typical example. 



Trinidad is a rectangular island, 

 with an area of about 2,000 square 

 miles, seperated from the eastern an- 

 gle of Venezuela and the delta of the 

 Orinoco by the gulf of Paria, and 

 bounded along the north side by a 

 bold range of mountains, which stand 

 like a wall between the lowlands on 

 the south, and the Carribean Sea, and 

 a long chain of volcanic islands on the 

 north. 



Asphaltum usually accompanied by 

 mineral tar and petroleum, occurs at 

 many points on Trinidad, and also on 

 the adjacent main. The largest and 

 most interesting deposit, not only of 

 this region, but of the world, is that 

 known as the Pitch Lake. This is on 

 Point La Brea (Spanish for "the 

 pitch"), in the southwestern parts of 

 the island, and one mile from the 

 Gulf of Paria. 



The topography of the country about 

 the lake is extremely simple. From 



three sides, north, west and south, the 

 land slopes gradually upward from the 

 sea to the surface of the lake which 

 lies one hundred and forty feet 

 above the gulf; while on the east the 

 land is slightly higher than the lake, 

 which therefore differs from ordinary 

 lakes, in resting, not in a valley, but 

 on a hill-top. In fact, its appearance 

 is as if the broad-mouthed crater of a 

 low-lying volcano were overflowing 

 with sluggish streams of black lava 

 slowly creeping down toward the sea. 

 These slowly moving masses present 

 curved lines and convex surfaces; and 

 Canon Kingsley has very aptly likened 

 them to glaciers, the lake represent- 

 ing a iiier dc glace. 



The asphalt becomes harder the 

 longer it is exposed to the air and sun, 

 and consequently the downward pro- 

 gress of the "black glaciers" must 

 constantly be checked, if not at last 

 entirely stopped. It seems impossible 

 to determine the extent of the over- 

 flow; for although the entire slope 

 from the lake to the sea appears as a 

 continuous sheet of pitch, yet it is 

 probable that most of this has exuded 

 from the asphaltic sandstone beneath 

 it. The area covered or underlaid by 

 this mantle of pitch is estimated at 

 3,000 acres. 



The bitumen is not injurious to 

 plant life, for the scanty soil covering 

 the pitch, and consisting largely of 

 that material in a pulverulent state, 

 supports a luxuriant vegetation. 



The village of La Brea, on the 

 shore, rests on the pitch; and the in- 

 habitants complain that their houses 

 are thrown out of level by the rising 

 and sinking of their tarry foundations. 

 It seems as if everything here — vege- 



