72 Proceedings of the Royal Society of Edinburgh. [Sess. 
fine sand and clay, and its chemical analysis is given by Mr Clifford 
Richardson as follows : — 
Total Mineral 
Matter. 
The finest Mineral 
Matter, separated 
from the Sand as 
far as possible. 
Per cent. 
Per cent. 
Si0 2 .... 
70-64 
32*36 
A1 2 0 3 .... 
17*04 
40*38 
Fe 2 0 3 .... 
7*62 
13*14 
CaO .... 
*70 
3*65 
MgO .... 
*90 
1-83 
Na 2 0 .... 
1*56 
K 2 0 .... 
*35 
*53 
so 3 
*97 
1*18 
Cl 
•22 
7T6 
100*00 
100*23 
This composition evidently indicates a certain proportion of argillaceous 
material, so that we may regard the 7 per cent, of non-bituminous organic 
matter as being not only due to inspissation, but also partly adsorbed in the 
inorganic 25 per cent. 
A specimen from the upper beds of the La Brea oil-sand, the parent oil- 
rock on the outcrop of which the lake has been formed, was taken from an 
exposure on the seashore near the lake, and gave on analysis the following 
interesting results : — 
Water, etc., volatile at 100° C. . . 5*24 per cent. 
Bitumen 15*10 „ 
Non-bituminous organic matter . 29*70 ,, 
Mineral matter .... 40*96 ,, 
100*00 „ 
Of the bitumen only 8 per cent., a little more than half, was soluble in 
petroleum ether, i.e. could be classified as malthenes. This bears striking 
testimony to the state of inspissation of the rock, and to the probability 
of a large percentage of the heavy residue having been adsorbed. 
This evidence of absorption and adsorption by argillaceous rocks, and of 
the effects of inspissation, points very clearly to the manner in which 
kerogen can be formed and preserved. Our definition of kerogen is 
“ organic matter, not petroleum or bitumen, but which will yield petroleum 
on distillation,” and on that definition we may claim that oils which by 
inspissation or adsorption have become insoluble in carbon-disulphide are 
in effect kerogen. 
That petroleum can be yielded by the distillation of these inspissated 
and insoluble products has been shown so often that no further proof is 
