— 7 Ba sah 3 a 
342 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
Girard’s analysis gives one-fourth of carbonate of lime ; but the loca- 
lities from which the specimens examined were obtamed are not 
specified,—a poimt that should always be attended to. At Thebes, 
the spangles of mica derived from the granites of Nubia and the first 
. cataract were perfectly distinct to the naked eye; but at Adfeh m 
the delta they were less numerous, and so comminuted as to be barely 
discernible with the aid of a lens. 
. The composition and texture of the mud is also subject to varia- 
tion from its proximity to, or distance from, the main channel of the 
j stream, where the coarser, heavier and more siliceous particles are 
usually found; while the finer and more argillaceous portions are 
| held in suspension, and carried out laterally towards the edges of the 
deposit by the gently overspreading waters. At particular pomts on 
/ the river’s course, where the inclination of its bed is great, and the 
current consequently rapid, as at the cataracts, the alluvium consists 
only of the very heaviest portions of transported detritus, mingled 
with the debris of the subjacent rocks ; and vice versd, where the m- 
| clination of the river’s bed is least, there we find the finest and most 
fertile deposit. It is a simple though remarkable truth im physical 
geography, that, had the surface of Egypt attained, m its upheaval 
from the waters of a former ocean, a greater inclmation towards the 
Mediterranean, that fertile mud, which exerted so wonderful an in- 
) 5 fluence upon the habits of the ancient population it attracted to the 
banks of the Nile, and which formed the foundation, the bed in fact 
of this ancient cradle of civilization to the modern world, would 
have been swept away, and buried beneath the waters of the sea,— 
useless at least to the races of mankind dwelling on the éarth’s sur- 
| face under existing conditions. 
| Few pebbles or “detritus of any size are found in the mud of Lower 
Egypt and the delta; and, as may be supposed, nothing but its fest _ 
and lightest ingredients escape into the Mediterranean, where I have 
observed the sea discoloured by them to the distance of forty miles 
from the shore. 
The northerly or Etesian winds that blow from the sea, varying a 
little to the E. and W. of N., nearly nine months during the year, 
(commencing by a curious coincidence with the inundation—about 
May,) by retarding the downward freshes, contribute materially to pre- 
vent the mud’s escaping to the Mediterranean, and to throw it upon 
the land. Added to this, these winds check the current at the estu- 
aries of the Nile by raising up the waters of the Mediterranean: hence, 
as the result of the opposing waters, are formed the banks of sand and 
mud by which some of the ancient embouchures have been silted up, 
causing the chain of back-waters and marine lagoons that frmge the 
present coast, in some of which we see alternate deposits of land and 
fluviatile testacea with marine remains, caused by successive imroads 
of the sea after it had been silted out at intermediate periods of less 
or greater duration. 
Striking evidence of the power of these winds in raising the waters 
of the Mediterranean on the coast of Egypt is afforded by General 
ie 
