18 79] Native Bitumens and the Pitch Lake of Trinidad. 235 
of a constant supply of oxygen. Now on the land, vegetation is 
constantly returning to the air the oxygen consumed by animals, 
but in the abysses of the ocean vegetable life is scarce or wanting, 
and hence it must result that over these greater than continental 
areas countless myriads of animals are living habitually en short 
rations of oxygen, and in water well charged with carbonic anhy- 
dride, the product of animal respiration. As a consequence, 
when these animals-die their tissues do not find the oxygen 
essential for their perfect decomposition, and in the course of 
time become buried, in a half decayed state, in the ever increasing 
sediments of the ocean floor. The same thing must happen to 
animals living in higher bathymetric zones, all the way to the 
surface, whose bodies sink to the bottom after death; they yield 
a little ammonia and carbonic anhydride, and then pass into the 
comparatively stable condition of a liquid or solid bitumen. 
During the lapse of ages these sediments, rich in organic matter, 
will be consolidated into limestones and slates, and at a later 
period may be elevated to form new land; a process which has 
been many times repeated in the past. (3) For, as geologists 
well know, rocks corresponding to those just described are of 
very frequent and extensive occurrence among the formaticns 
now exposed to their observation. 
Petroleum is usually associated with salt, the same well often 
affording both oil and a strong brine; a fact very suggestive of 
the marine origin of the petroleum. While the disagreeable 
smell of some oleiferous limestones is probably due, as remarked 
by Newberry, to the animal origin of the oil. 
The capability which the so-called bituminous coals possess of 
yielding, by a process known to chemists as destructive distilla- 
tion, various liquid and gaseous hydrocarbons, some of which 
resemble petroleum, a property common to most substances of 
organic origin, has not only led to their being erroneously 
regarded as bituminiferous, but many geologists have inferred 
that we have here a clew to the origin of the vast reservoirs of 
petroleum known to exist in this and other countries, and which 
have of late years been tapped with such astonishing results. 
Anthracite is undoubtedly a species of natural coke, produced 
when ordinary bituminous coal loses its volatile ingredients ; its 
general mode of occurrence and geological relations prove this. 
But is nature’s mode of making coke strictly analogous to what _ 
