59 
1915-16.] The Origin of Oil-Shale. 
In examining, then, a thick series in which both the carbonaceous and the 
petroliferous phase are to be observed, we should expect to find thick 
impervious beds separating the two phases. In the Yaw River section in 
Burma and in many coast sections in Trinidad this holds good. 
The strata of a thick series may be found to be of the same type 
throughout — rapidly alternating estuarine and deltaic sediments, with occa- 
sional marine bands, — yet the upper beds may be coal- bearing and the lower 
oil-bearing. The only differences in environment of which we can be sure in 
such a case are that the lower beds must have been subjected to greater 
pressure and a slightly higher depth-temperature. 
Where thick impervious beds do not intervene between the two phases, 
we frequently find them overlapping, so that for a certain thickness of 
strata oil seepages and coal outcrops may alternate, and a bed may be both 
lignitic and petroliferous. This is to be seen to great advantage in Estado 
Falcon near the north coast of Venezuela. The lateral passage of a lignitic 
group into an oil-bearing group has also been described in Trinidad, Assam, 
and Burma. In such cases, and also in cases of the alternation of the petrol- 
iferous and carbonaceous phases, the former is found in argillaceous en- 
vironment, and especially capped by impervious strata, and the latter 
in arenaceous environment. 
These facts are sufficient to suggest that oil-bearing strata bear some- 
what the same relation to coal-bearing strata that oil-shale-bearing strata 
do. It may be mere coincidence, or there may be something essential 
in the relation. 
To prevent any misunderstanding it must be pointed out that if it be 
granted that petroleum and lignite or coal can be formed from the same raw 
material, there is evidence that once the lignitic or coal stage has been 
reached no conversion into oil is possible short of destructive distillation. 
Sections in the younger Tertiaries of South America and Trinidad illustrate 
this point. In one a lignitic seam is exposed on the foreshore with tree 
roots in position of growth in the underclay. The tree trunks are lignite 
in the seam, and parts of the roots are lignitic, but the greater part remains 
wood. A section near Caoderalito in the district of Buchivacoa in Venezuela 
supplies another link. The strata are dipping at 30° and are somewhat 
above the middle of a Tertiary series of about 8000 feet in thickness. In 
a band with somewhat confused bedding several flattened tree trunks are 
preserved as lignite, while the rest of the band is petroliferous and gives 
rise to a seepage of asphaltic oil. A thin underclay is beneath the band, 
while above it is some 10 inches of clay followed by 3 feet of oil-sand, the 
whole being surmounted by a thick argillaceous band. It is suggested that 
