OBSERVATIONS. 
367 
with magnesia, and distinctly referrible to similar strata that 
form subordinate beds in the new red sand-stone formation of 
England ; and they seem to occupy a similar position in the red 
sand-stone of the desert plains that lie on the north and south side 
of the basaltic chain of the Black Mountains in Fezzan. 
9,6. A pudding-stone, composed of pebbles of dolomite, united 
by a granulated calcareous cement. Taken from a Roman castle 
at Bonjem. The surface of this specimen has the same glossy 
polish which has been before mentioned in some others. 
27. Specimen of the materials of which the Castle of Zuela and 
tnany other old castles are constructed. It is an artificial com- 
pound, made up of small grains of quartz of the size of millet seed, 
imbedded in a cement or paste of yellowish marl, which effervesces 
rapidly with acids : there is no more marl than is sufficient to hold 
together the grains of quartz. Buildings are constructed of this 
material by pressing the composition into cases, which are re- 
moved when it is dry. 
e 28. Milk-white compact carbonate of Ume. From the plain 
between the Black Mountains and Pass of Kenair. It is beauti- 
fully furrowed over with small channels and grooves, Hke No. 18 
and 19. 
29. White limestone, of coarser grain. From ditto. 
80. White limestone, filled with grains of fine white quartz. 
From ditto. 
31. Wliite limestone. From the north base of the Black 
Mountains. 
S2. Compact yellow carbonate of hme, having a polished glossy 
surface, beautifully furrowed, and resembling a bit of yellow bees' 
wax. From the north base of the Black Mountains. 
These last specimens of carbonate of lime are found with those 
of dolomite described immediately before, and seem to belong to 
the same formation with them. 
