Arabian 
chain. 
Cliffs of 
344 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
farther removed from the reach of calculation. Near the edges of the 
alluvium, the sands of the desert, on the west bank of the Nile more 
particularly, are blown upon, and intermingle with, the deposit thrown 
down bythe river. Hence the uncertainty of all calculations on the pro- 
gressive rate of the increase of soil generally throughout Kgypt within 
given periods of time, and grounded on the rate of its actual accumu- 
lation around the bases of certain buildings, statues, nilometers, &c., 
in particular localities. It may be added too, that the alluvium 
around the bases of most of these monuments has not remained un- 
disturbed during its progressive increase for the last 3000 years by 
the annual plough or spade of succeeding generations of cultivators ; 
nor has it, in most cases, been proved at what period the Nile actually 
reached these bases, whence the progressive amount of deposition 
must be dated, and not before. 
Upon such uncertain data the French savans under Napoleon cal- 
culated the progressive vertical rise of the soil throughout Egypt at 
about four inches per century. 
From the circumstance of the deposit being greater near the stream’s 
channel than at a distance on each side, it presents a raised bed, the 
most elevated portions of which are not under water at high Nile, and 
of which the following diagram (fig. 5) may serve to convey an idea. 
Fig. 5. 
Alluvial rocky soil. Channel of Nile at low water. Alluvial Me soil. 3 Es oa 
ras 5 
aad 
HS 
Surface covered by inundation. ‘ 
Gr rane Extension of Nile Mud.—Judging from the thickness of 
the annual layers exposed in cliffs of Nile mud, of which I have 
counted upwards of 900, the amount of alluvium annually deposited 
has not varied in the aggregate for the last 1000 years, and it is 
highly probable that both the periods and amount of the inundations 
haye not suffered any material change smce the present physical con- 
ditions of the country were established. It is clear therefore that the 
surface, which the waters overspread, must be gradually elevated by 
such periodical depositions ; and, as the surface rises, the level of the 
inundations must rise also, and continue to overspread, where not. 
confined by vertical banks, a superficies gradually increasing with the 
amount of matter deposited by the floods. . 
Similar difficulties exist in attempting to calculate the progressive 
rate of the increasing superficial extent of alluvium throughout Egypt, 
as in determining that of its vertical rise; added to which, the effects 
of the drifted sands from the Libyan Ag in curtailing its apparent 
limits, to be alluded to in the concluding portion of this paper, are to 
be satisfactorily ascertained and taken into consideration. 
That such a progressive vertical and horizontal mcrease does ac- 
tually occur, has been clearly proved by Sir G. Wilkinson* from the, 
fact of the inundations now covering to some depth the bases of. 
statues, &c., known at certain periods of history to have been be- 
* Journal of Geograph. Soc. of London, vol. ix. 
