636 ANCIENT FLUVIATILE DEPOSITS 



quartz-grains and pebbles, cemented by ancient mud, form- 

 ing a kind of sandstone-grit, and yielding calcareous and 

 marly concretions. 



3. Ancient Nile-mud, indurated, and containing embedded 

 iron shot clay, siliceous limestone, &c, full of calcareous 

 and marly concretions in the ferruginous portions. 



4. Fine and coarse quartzose conglomerate, with the 

 materials united by ancient Nile-mud and calcareo-argilla- 

 ceous cement, very hard, used as a building stone, and con- 

 taining embedded masses of saline clay and of ordinary clay 

 and marl, full of clay ironstone, ferruginous sandstone, and. 

 of calcareous and marly concretions. 



5. Freshwater limestone (travertine, or slab kankar ?) of a 

 dark-grey colour, hard and sonorous, occasionally having a 

 marly appearance, with here and there a tendency to a con- 

 centric and generally crystalline structure. 



The beds are described as horizontal, of very variable 

 thickness, attaining sometimes, in Nos. 1, 2, and 3, as much 

 as five or six fathoms (Jahrbuch, 1838, p. 408). According 

 to Eussegger, with the exception of the uppermost deposit, 

 they contain very generally fossil vegetable remains, chiefly 

 the wood of Mimosas (Mimosa Nilotica) and stems of Asclepia 

 (Galotropis) procera ; the former are either converted into 

 lignite or have their core exhibiting a concentrically disposed 

 and radiating crystalline structure, derived from the embed- 

 ding matrix ; the latter have the bark preserved, but the 

 spongy core occupied either by calcareous matter or con- 

 glomerate. These alluvia presented very commonly shells of 

 the Mollusca now living in the waters of the Nile, both bi- 

 valves and univalves, together with some land species. 

 Among the most common was Mtlieria Caillaudi, occurring 

 frequently in heaps or oyster-banks, together with species of 

 TJnio, Iridina, and Anodonta. In the alluvium of Sennaar he 

 found Ampullaria ovata and a species of Helix. He adds, 

 that JEtheria Caillaudi was also abundant in the deposits of 

 the White Nile. 



M. Lefevre, writing at the same time, confirms the obser- 

 vation of Eussegger about the occurrence of the conglome- 

 rate. ' Near Khartoom, on the Libyan side, you meet on 

 the redans of the White Nile with a modern conglomerate 

 composed of fragments of sandstone united by a calcareous 

 cement, either deposited by the water of the river or filtered 

 through the alluvial soil. This concretionary deposit is ex- 

 hibited equally on the banks of the Blue Nile, and it is well 

 seen on either side where the banks are perpendicular.' He 

 adds that the alluvial escarpment is nowhere higher than 

 from 50 to 56 feet. 



