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from water near the surface. In this connection, it is intereslin{j to note thai 
the once famous Bathyhius, a flocullent material l^rought up fr'om more tlian 
1000 metres in depth in the Atlantic, was proved hy Buchanan [Proc. Boyal 
Society, XXIV) to be amorphous sulphate of lime precipitated hy the alcohol 
employed. 
The subject is undoubtedly a very complex one, and the following facts from 
the chemical and geological side have to be kept in mind in framing a reply. 
1. As already stated, the Egyptian Nitrates extend over a wide area, and 
are connected with a definite geological horizon. 
2. They occur in clays which by their relations to the rocks underlying and 
overlying them are obviously the finest materials derived from land under- 
going depression. They form, in fact, a transition series between a great mass 
of Limestones (built up of organisms) above, and an equally important series 
of Sandstone below. 
3. If the Nitrates were due to geological conditions in the past, we should 
have to seek for specially favourable circumstances for their accumulation in 
deep-sea deposits. On the other hand, we should have to assume that these 
compounds (usually highly soluble) or materials capable of conversion into 
nitrates had been retained in the clays through long periods of time, as the 
strata are, on the evidence, of great geological age. 
On the Chemical side we have to remember 
/|. That Nitrates are mainly produced in soils (so far as at a present known) by 
the action of Nitrifying Bacteria or connected with Decomposing Organic Matter. 
5. As regards Nitrifying Bacteria, circumstances favourable to their activity are 
Moisture, Darkness, Free aeration, and a base to neutralize the acids pro- 
duced. The best temperature is 3 7° G. and they are inactive below two-thirds 
of a metre in the sub-soil (Hall) or from one to two metres below the surface 
(Wiley). 
6. Unfavourable to their activity are Dessication, Temperatures below 5° and 
above 55°, and strong light. 
We are at once face to face with the following difficulties demanding 
research : 
a. No Nitrifying bacteria have been proved to exist in these shales, but, 
on the other hand, they have never been sought for, so far as I am aware. 
a 1 
