OBSERVATIONS. 
S65 
8, 9, 10. Ferruginous concretions, forming aetites or geodes 
in the red sand shore. The broken fragments are compact, 
sonorous, and of a dark hver colour, having a shining polished 
surface. The sand which formed their matrix still adheres to the 
exterior of some of them. They occur on a plain and a mountain 
near Om el a Beed. In lat. 27° -73 : they are here so abundant, as 
almost entirely to cover the ground, and impart to it a dark red 
colour. This accumulation of them probably arises from the wind 
having drifted away the fine sand, in which they were formed, 
leaving behind the heavy bodies in question. 
A little farther north, at the foot of the Pass of Kenair, near 
some steep sand hills, is a narrow bed almost entirely composed of 
tubular concretions of iron of similar origin, irregularly ramifying 
through the sand like roots of trees, and producing a rugged ap- 
pearance, which at first sight resembles a bed of lava. 
11. Flat lamina of variegated sand stone, held together by a 
calcareous cement, and covered on each side by small spherical 
tubercles closely studded by the side of each other. Similar con- 
cretions are common in the imperfect beds of sand stone strata of 
all formations. 
12. Flesh-coloured marl, full of small irregular crystals of 
selenite. The colour of this marl resembles that of the rock marl 
of England : it is from a plain near Gatrone, lat. 25°. 
13. Fibrous gypsum passing into foliated, apparently from a 
matrix of ochreous marl stone. 
14. Crystals of calcareous spar imbedded in yellow-ochre. 
Found with No. 13, in the same mountain with the Calcaire 
Grossier, No. 4, thirty miles south of Benioleed. 
15 and 16. Fibrous and fohated gypsum from a similar matrix 
of ochreous marl to No. 13 and 14, and found on the same plain, 
near Bonjem, with the two species of cardium, No. 3. 
It is probable these last four specimens come from a stratum 
