PROF. EHRENBERG ON FOSSIL INFUSORIA. 411 



from Kosemitz as a white meal, and filling out its internal cavities 

 might partlj- belong to the still existing genus Pyxidicula. 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 

 scarcely be an optical phaenomenon, and which are covered by a trans- 

 parent siliceous matter. There are sometimes seen in the latter, as in 

 the Gailhnetta varians of Cassel, radial stripes proceeding from a pierced 

 centre to the periphery, and also somewhat plainly a separate defined 

 shell. The chalk-like envelojie 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 metamorphosino- 

 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 Holothurise 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 fonnation 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 oj)al, and found that a mass similar to Steiinnark (lithomarge) 



Vol. I. — Part III. 'i f 



