77 
1915-16.] The Origin of Oil-Shale. 
An interesting passage may be quoted here from the Geological Survey 
memoir on The Oil-Shales of the Lothians, p. 165: “As already indicated, 
the crude oil diminishes and the ammonia increases, as a general rule, with 
the age of the shale. In old peat the proportion of nitrogen is sometimes, 
if not always, greater than in new peat of the same bog, owing to the 
nitrogen-free compounds decaying more rapidly than the nitrogenous com- 
pounds under the special circumstances. Recent plants subjected to de- 
structive distillation yield a very acid distillate, peat less so, brown coal 
still less ; Torbanehill mineral has a distillate slightly acid at the beginning 
and alkaline further on, while shale is very alkaline throughout. Hence 
the decrease of crude oil and increase of ammonia may partly be the result 
of age. No doubt part of the nitrogen is in combination in the kerogen, 
and this part may through time have increased in proportion; but the 
richness of the oldest shales in ammonia is more than we would expect 
from this cause alone.” 
The percentage of sulphur is another interesting point the importance 
of which will be seen later. 
All crude petroleum contains a proportion of nitrogen, though it is often 
so small that it is seldom estimated. Sir Boverton Redwood, in Petroleum 
and its Products, gives the percentages of nitrogen in oils from many 
different fields on the authority of Beilby, Peckham, and Mabery. Thus 
Galician oil has been shown to contain T88 per cent, of nitrogen, and 
Pennsylvanian oil occasionally as little as ‘008 per cent. Oils from Ohio, 
West Virginia, and Baku have given on analysis percentages of ’230 per 
cent., '540 per cent., and '05 per cent, respectively. 
Californian oils, which as a rule are heavy, asphaltic, somewhat in- 
spissated, and rich in unsaturated hydrocarbons, give considerably higher 
percentages, rising to slightly more than 1 per cent, among the heavy 
malthas. Thus percentages of 1T09 per cent., 1*016 per cent., and 1*08 per 
cent, are recorded from oils of the Heywood Petroleum Company, Pico 
Spring and Canada Luca in California. 
It seems to be established that the nitrogen occurs, to some extent at 
least, as pyridine bases. 
It is noteworthy that the heavier and more inspissated the oil the 
larger the nitrogen and sulphur percentages become. It is evident, then, 
that these elements, in whatever manner they are combined with hydro- 
carbons, are associated with the heavier and more complex molecules. The 
heavy oils of the Texas field, containing sulphur percentages of 3 per cent, 
or over, require special refining processes. 
