— 162 — 
h. If nitrates are forming at present, as dessication and strong light arc 
unfavourable, and rainfall small, we must postulate the existence oî dew to 
afford the necessary moisture. This means a second line of study as yet largely 
untouched. 
c. If the dew supply be not siifTicient or organisms absent, we have to fall 
back on the assumption of a higher rainfall in the past, for which there is 
evidence from many sources. 
(I. If it were argued that the shales have come under the influence of the 
Nile (or streams connected with it) when it was flowing at higher levels than 
at present, we have to face the fact that nitrates have been recorded both in 
Kharga Oasis and West Sinai, indicating that the full explanation is not in 
tiiat direction. 
If, on the other hand, we search for light from the chemistry of deep-sea 
waters and deep-sea deposits, we are faced by serious gaps and contradictions 
in our enquiry. It must suffice to mention a few facts of deep interest and 
possible significance for our study. 
e. Existence of Nitrates in Sea Water. — Messrs. Purvis and Coleman 
[Journ. Roy. Sanitary Inst., vol. XXVII, n° 8, kjoG, p. /i33)f') were led to 
the conclusion that nitrates" do not exist in sea water, but this view was sub- 
sequently disputed by Messrs. Gopeland and Soper [Eight International Congress 
of Applied Chemistry, vol. XXVI, p. 91 1-2 1 3). The amount of nitrogen found 
as nitrates was shown to be present in land, harbour, and sea-water in the 
following proportions : 
Land Water o.oo4 lo 0.366 pails per million. 
Harbour Water o.i25too.56o — — 
Sea Water 0.100 to o.aOo — — 
The quantities are undoubtedly minute, but no details are given regarding 
depth. 
f. Important work on Nitrification and Denitrificalion has been carried out in 
another direction by W. Mair (On the Role of Bacteria in the Biological Methods 
of Sewage Purification, with special reference to the Process of Denitrification. 
Full references not available. 
