32 GEOLOGICAL MEMOIRS. 



the British Isles is stated by Sir R. Murchison to be in Lower 

 Silurian rocks. 



From these resemblances, which are unfortunately founded on a 

 very small number of species, the author thinks himself justified in 

 concluding, that the lower group (C) of the middle Bohemian division 

 corresponds to the lowest fossiliferous beds of Great Britain — to 

 those namely which contain Agnostus. 



The author states that he shall afterwards have occasion to explain 

 why he excludes at present the other beds above the Llandeilo flags. 



3. In Sweden and Norway, the Paradoxides Tessini and Agnostus 

 pisiformis offer the same elements of comparison Avith Bohemia, since 

 these two species are also the only ones that can be identified among 

 the fossils of this kind in the two countries. They both belong to 

 the alum schists which form the base of the Silurian system of 

 Scandinavia, considered by Sir K. Murchison as the beds corre- 

 sponding to his Llandeilo flags. The author concludes that this 

 group (C) is on the same geological horizon as the most ancient 

 fossiliferous series of Sweden, Norway, and the British Isles. It 

 forms, therefore, the base of the protozoic rocks, as recently defined 

 by Prof. Sedgwick. 



Group D. — 1. Geological characters. — Most of the rocks of this 

 group contain a large proportion of silex. The abrupt passage from 

 the dark schists to these siliceous conglomerates and white quartzites 

 is distinctly seen in the valley near Ginetz. The beds are conform- 

 able, or very nearly so, although at first sight this appears not to be 

 the case. 



The lower member of this group chiefly consists of siliceous schists 

 varying in colour, above which appear thick beds of coarse con- 

 glomerate. Still higher very fine quartzites are found, and at the top 

 appear black and very fissile schists, including, but much less com- 

 monly, bands of quartzite. 



It is worthy of remark, that from the base of the azoic rocks to 

 the upper part of the present group of formations, there are no re- 

 markable limestone bands. The author possesses only a single frag- 

 ment of rock of this kind, found in the middle of the quartzites, and 

 containing the head of a Trinucleus ornatus. He could never dis- 

 cover the bed from which this came. Other indications of limestone 

 in very thin beds are met with near Prague, with impressions of 

 trilobites among the quartzites of this formation. M.Zippe has men- 

 tioned the fact, but the author states that he has searched in vain to 

 discover the bed, which is probably only a lenticular mass. 



The calcareous element was therefore absent during the formations 

 hitherto described. 



2. Palceontological characters. — The author describes twenty-five 

 species of trilobites, which occur only in the upper beds of the 

 quartzite and in the schists superimposed. The lower beds of 

 quartzose sandstone, and the conglomerate and siliceous schists which 

 form the base of this group (D), have not yet afforded any trace of 

 organic beings. Of all the fossils described, one only, Trilobites 

 Lindaueriy belongs to the lower beds. 



