— 167 — 
point out the complexity of the problem, and the many factors involved with- 
out presenting a solution. It may, however, be useful alike to agricultuialisi , 
chemist and geologist to know what results liave been already attained, serv- 
ing as a basis for new lines of study. Possibly the best of these would be an 
accurate topographical survey of a selected area, accompanied by systematic 
collection and chemical examination of samples of the shales. 
GENERAL SUMMARY. 
1. Tfie Nitrate Shales in the Nile Valley have as a rule yielded an average 
of 5 o/o or less of Sodium Nitrate on analysis. 
2. They are capable of enrichment, the difficulty in their commercial deve- 
lopment being their variabih'ly in distribution, not their low nitrate content. 
3. The Nitrates are present at a definite horizon in the geological series, 
forming part of the uppermost Cretaceous strata (Esna Shales and Ash-grey 
Clays). They have been traced from Farafra Oasis to West Sinai, and nitrates 
have been recorded in them both from the latter locality and from Kharga 
Oasis. 
U. Their wide distribution at the same horizon suggests that the nitrates 
represent compounds formed or absorbed at the time of deposition of the 
shales, but the character of which require further study. 
5. On the other hand, the presence of Sodium Nitrates being only marked 
near the surface suggests that they are either formed by some means now 
acting, such as nitrifying organisms working under moist conditions of the 
soil, or have been drawn to the surface by capillarity. 
W. F. Hume. 
