70 
Proceedings of the Royal Society of Edinburgh. [Sess. 
at the surface there is a percentage of this insoluble material, and the 
percentage seems to depend upon the degree of inspissation and on the 
impurity in the shape of inorganic matter present, especially if the in- 
organic matter be of an argillaceous nature. Thus we have seen that a 
Barbados manjak of presumably Tertiary age may contain less than 1 per 
cent, of this insoluble material, while an albertite of Devonian age may 
contain 90 per cent. 
Similarly, in a manjak vein from the College Mine in Barbados at a 
depth of 60 feet we find a distinct difference between the columnar selvage 
of the vein and the centre as follows : — 
Columnar 
Selvage. 
Centre 
(conchoidal 
fracture). 
Water and volatile matter at 100° C. 
1-20 
2T6 
Ash 
*44 
•44 
Bitumen ...... 
96-00 
97-40 
Organic matter not bitumen . 
2-36 
nil. 
100-00 
100-00 
That the state of inspissation is much higher in the selvage than in the 
centre of the vein is proved by the percentages of malthenes, which are 
18*20 and 35*60 respectively. The analyses are by Professor Carmody, 
Government analyst of Trinidad, and the two samples are taken from 
within a few inches of each other. The conchoidal variety is probably a 
later intrusion. 
Much similar evidence from manjak veins in Trinidad could be adduced, 
but the point is quite clear that as the material weathers, as shown by the 
decreasing percentage of malthenes, the percentage of insoluble matter 
increases. 
A very pure asphalt formed by the inspissation of oil from a seepage in 
the Guapo field, Trinidad, analyses as follow : — * 
Water and matter volatile at 100° C. . 18-50 
Bitumen 8040 
N on-bituminous organic matter . . *86 
Ash . . *24 
100-00 
The malthenes in this case amount to 71 per cent. The percentage of 
“ organic matter not bitumen ” cannot in this case be adsorbed , as the 
* This analysis and those that follow are by Professor Carmody. 
