1838.] 



Prof. Ehrenberg on Fossil Infusoria. 



161 



It was natural for me now to test again the fiint 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 

 specimens are very similar to the striped semi-opals. They all con- 

 tain spherical and often needle-shaped bodies, at times with apertures, 

 which can scarcely be an optical phsenomenon, and which are covered 

 by a transparent 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 eflfervesce 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 dis- 

 solving or metamorphosing matter, but not completely penetrated by 

 it. According to this the flint would be formed nearly in the same man- 

 ner as the semi-opal of the Polirschiefer. The siliceous parts of the 

 chalk would, from their specific gravity, accumulate in certain places, 

 and form layers of siliceous Bergmehl in the chalk ; in the same man- 

 ner as we see in high perpendicularly cut heaps of rubbish, things of 

 the same specific gravity, mortar, pieces of porcelain, bones, &c., ar- 

 ranged 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 at- 

 tracted the special attention of geologists, and of which some at times 

 take the form of Holothurise and corals ; the greatest number however, 

 partly on account of their enormous volume and partly from their whol- 

 ly 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 primi- 

 tive 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- 



