PROF. EHRENBERG ON FOSSIL INFUSORIA. 411 
from Kosemitz asa white meal, and filling out its internal cavities, 
might partly belong to the still existing genus Pyazdicula, They are 
quite different from the stalactitic columns which produce the round 
eyes in agate. 
It was natural for me now to test again the flint of the chalk, which I 
had before often examined: and this time I employed a higher power, 
and therefore with more success. The black flint, which broken into 
small pieces is transparent, showed no evident traces of an inclosure of 
microscopic organic bodies, but such are easily perceptible in the whit- 
ish and yellowish opake pieces. The more rare horizontally striped spe- 
cimens are very similar to the striped semi-opals. They all contain sphe- 
rical and often needle-shaped bodies, at times with apertures, which can 
searcely be an optical phenomenon, and which are covered by a trans- 
parent siliceous matter. There are sometimes seen in the latter, as in 
the Gaillonella varians of Cassel, radial stripes proceeding from a pierced 
centre to the periphery, and also somewhat plainly a separate defined 
shell. The chalk-like envelope and white covering of the flint does not 
effervesce with acids, and is therefore not chalk, but silica, as I have 
convinced myself; it does not appear to originate in decomposition, but 
is like the meally covering of a lump of dough ; that is to say, it is that 
layer of siliceous meal (of evident organisms) which at the formation of 
the flint has only been touched by the dissolving or metamorphosing 
matter, but not completely penetrated by it. According to this the flint 
would be formed nearly in the same manner as the semi-opal of the Po- 
lirschiefer. The siliceous parts of the chalk would, from their specific 
gravity, accumulate in certain places, and form layers of siliceous Berg- 
mehl in the chalk ; in the same manner as we see in high perpendicularly 
cut heaps of rubbish, things of the same specific gravity, mortar, pieces 
of porcelain, bones, &c., arranged separately in stratified horizontal 
layers. If now a dissolving elastic or other fluid forced its way into the 
heap, those, nodules must also be formed in horizontal layers and nests, 
which have-already attracted the special attention of geologists, and of 
which some at times take the form of Holothuriz and corals ; the great- 
est number however, partly on account of their enormous volume and 
partly from their wholly undetermined forms, present great difficulties 
to this hypothesis. In the Menilite the nodule formation of a penetrating 
substance, itself occupying scarcely any space, and not changing the 
layers of the primitive mass, is particularly well seen. 
I have finally to mention the examination of the precious opal of 
Kaschau. In some fragments both of the common serpentine opal of 
Kosemitz and of the precious porphyry opal of Kaschau, I saw also in- 
closed round bodies like those in the flint ; the greatest mass was how- 
ever in the interior homogeneous. I examined the matrix of the pre- 
cious opal, and found that a mass similar to Steinmark (lithomarge ) 
Vor. I.—Parrt III. ZF 
