PITCH, ASPHALT, ROCK-OIL. 191 



The pitch is everywhere hardened into asphalt from the 

 evaporation of the oil, except in the centre, and its highest 

 temperature does not exceed 35 C. (95 Fahr.). There is 

 no evidence of any volcanic eruption close to the lake ; but 

 there is an active mud-volcano twenty miles off, and 

 the mainland is often shaken by severe earthquakes, so 

 that in all likelihood the pitch is derived from beds of 

 vegetable matter, which are being slowly distilled by volcanic 

 heat. A mile or two off there are beds of brown coal, one 

 of which, if continuous, would pass beneath the lake at a 

 great depth ; and when it is considered that for ages past 

 the Orinoco has been rolling down vast quantities of 

 timber and vegetable matter, it seems highly probable that 

 these are the materials from which the pitch is made. It is 

 certainly derived from decayed vegetable matter, and sticks 

 which drop into the liquid pitch are often found partially 

 transformed into the same substance. 



Another product of the decomposition of vegetable 

 matter is rock-oil or petroleum, which is found in many parts 

 of the world. Bituminous shales i.e., hardened mud im- 

 pregnated with vegetable matter are also made to yield oil, 

 and thus, thanks to the way in which we have learnt to 

 utilise nature's refuse, estates formerly worth but a few hun- 

 dred pounds a year, now bring in as many thousands. 



There are about a hundred petroleum wells in Burmah, 

 and there is one in Zante which has been flowing for 2,000 

 years ; but petroleum was not discovered in America and 

 Canada until 1861, in which year it was mentioned as an 

 important fact that 250 barrels were exported. And im- 

 portant it undoubtedly was, for by 1882, the exports 



