162 EGYPT. 
petrified palm-tree, of which Mr. Cripps had col- 
lected a very great variety. They found these 
uons'^"'^' masses lying in detached fragments among the 
loose sand, wholly disengaged from any other 
stratum, and scattered over the face of the 
desert. In the same manner, but more fre- 
quently, appeared the large pebbles of Egyptian 
jasper, being almost always of a flattened 
ovate shape. This mineral is too well known to 
require a more particular description ; but who 
Doiihtini can explain its origin ? The received opinion, 
£i^^ptian and that which daily experience confirms, re- 
jaspcr. specting siliceous concretions in general, is this, 
that they have been deposited, after a stalactical 
process, in the fissures and cavities left by air 
in substances of anterior formation. Admitting, 
therefore, that every one of these Egyptian peb- 
bles once occupied such cavities, in strata now 
reduced to a pulverized state, and since become 
the sand of the desert, what idea can be formed 
of the antiquity of this kind of jasper P Unlike 
other flinty substances, it seems to be almost 
incapable of decomposition by exposure to the 
atmosphere ; having, as an exterior crust, a thia 
mvestment of a reddish brown colour, which 
differs in appearance only from the nature of the 
stone itself; its chemical constituents being 
precisely the same. Masses of pure silex. 
