— 166 — 
to build up new organic substances or ammonia. Consequently they do not 
appear in the Red Sea. Out of 38 samples examined, 18 showed no coloura- 
tion and 3 very slight indications. In the Gulf of Akaba, on the other hand, 
the indications were more marked at the 100 metre level, the colour in seven 
cases attaining a very faint blue (n° 6 on Dr. Natterer's colour scale). 
In the main Red Sea, of 36 analyses, sixteen gave no result, twelve the value 
1 on scale (marked trace of violet), six the value 9 (very faint violet), and 
two the value 5 (trace of blue). These latter were in the northern part of the 
gulf, but the higher results may be due to the samples having been collected 
in winter. 
SUMMARY OF FACTORS FAVOURARLE TO COLLECTION 
OF NITROGEN-CONTAINllNG SALTS IN SEA-WATER. 
From the above discussion we are led to conclude that the following factors 
are favourable : 
The presence of still walei", fiee of currents, not exposed to sunlight, with 
absence of denitrifying bacteria; and it has also been seen that experiments 
up to the present only suggest such conditions being realized at depths of over 
200 to aSo fathoms. 
Further, as clay is an excellent absorber, the very fine material of this 
nature settling down on the bottom of a still sea might fairly be assumed to 
take up part of the nitrogen-containing salts, and the question arises whether 
they would remain connected with the clays during long geological periods 
until exposed by earth-movements. This question can only be determined by 
testing shale taken at some depth below the surface for nitrogen compounds. 
Mr. Hughes, to whom I submitted these notes, has pointed out that these 
nitrate shales may stand in intimate relation to the phosphate beds which 
they overlie. The INitrates must have been abundantly present when the fish 
remains forming the phosphates were being deposited. The more soluble 
nitrates might have been absorbed by the clayey materials carried out seaward 
by streams from the land, and been preserved until denudation exposed them. 
Then rainfall and subsequent ascension by capillarity during evaporation 
would bring them to the surface layers. It is only possible at present to 
