338 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
the calcareous matter with which it is charged from the limestone 
rocks it passes over: portions of the gravel so agglutinated resemble 
a hard pudding-stone. 
In several places, resting immediately on the calcareous cliffs lane 
ing the Mediterranean between Alexandria and Aboukir, near Ceesar’s 
Camp, I observed a bed a foot thick of bleached human fanaa derived 
from the ancient Roman and Greek cemeteries, intermingled with the 
bones of those slain in the various modern sangumary conflicts that 
have taken place among the neighbouring sand ‘hills. " The bones are 
covered by a layer of sand and gravel, varying from a few inches to 
3 or 4 feet in thickness. They appear to have been washed into their 
present position by the drainage-water running from the higher 
grounds to the sea, and, though in an excellent state of preservation, 
are not fossilized. The supermcumbent sand and gravel has im some 
places been agglutinated, together with fragments of ancient buildings, 
by carbonate of lime and ferruginous matter deposited by the drainage- 
water. 
Drift and Erratic Detritus.—The saline sands and gravel that 
constitute the deserts of Egypt, overspreading all the stratified forma- 
tions, appear to have been deposited on a sea-bottom, as they cover 
marine formations. Pelagic remains have been found imbedded ; 
and according to M. Linant, fossil bones: but it has not been clearly | 
ascertained whether the former have not been derived from the 
subjacent fossiliferous rocks. This drift and detritus not only fill 
up chinks and hollows in the rocks below, but cover the tops and 
sides of mountains. In many places the pebbles composing them 
have been transported from considerable distances ; for mstance, the 
gravel beds from 1 to 10 feet thick covering the raised coral beach 
of Kossier, and the limestone cliffs of Abu Mungara skirting the 
Red Sea near the Jaffatine group, and the drift resting on the elevated 
platform of the Libyan desert near Dendera. In all these localities 
the gravel consists of rolled pebbles of the distant plutonic and meta- 
morphic rocks, mingled with those from the rocks in the vicinity, 
such as quartz, chert, jasper, agate, silicified wood, &c. At Abu 
Mungara I observed a pebble of reddish marble, resembling that of 
Verona, with imbedded crystals of sahlite. From the great quantity 
of rolled, and partially rounded, fragments of silicified wood found 
scattered in the desert sands, I am inclined to believe that much of 
the detritus composing them was derived from the subjacent sand- 
stone, whose continuity has been greatly impaired by denudation, as 
already stated, and in which the silicified wood is invariably found 
imbedded. It is further worthy of remark, that though beds of 
gravel and sand transported from great distances are not unfrequent 
(pebbles from the rocks of Upper Egypt and Nubia are found near 
the Mediterranean in the valley of the Bahr bila Maieh), still the 
nature of the composition, and sometimes the colour of each particu- 
lar portion of the desert, is generally much influenced by the charac- 
ter of the rocks in the immediate vicinity. The sands of the Nubian 
desert, where granite and sandstone abound, are granitic and siliceous ; 
and, according to the observations of Ehrenberg*, destitute of the 
* Lond., Ed. and Dub. Phil. Journ. vol. xviii. pp. 385, 386. 
