FACTS AND OBSERVATIONS. 



XXV 



The stage F is also in two parts, F. f. 1 and f. 2. It consists of pale and dark-tinted lime- 

 stone, neither concretionary nor fetid, but with much chert, either disseminated or in kidneys. 

 Organic remains become much fewer here, with the exception of Brachiopoda, which are numerous. 



The stage G is 1000 feet thick, and in three divisions. It is composed of argillaceous lime- 

 stone in thick beds and with chert (as in stage F), with calcareous lumps lying in clay schists, 

 which last, increasing in quantity, gradually excludes the calcareous element, and ends in stage H. 



The stage H is 850 feet in average thickness, and is in three parts. This highest stage is 

 principally clay schist, grey, green, black, alternating with beds of impure quartzite. The tran- 

 sitions from part to part and from stage to stage are very always gradual. 



The Silurian population about Prague is unique; no other country can show anything 

 resembling it. . So great is the buried multitude, that this vicinity might be supposed to be the 

 common sepulchre of marine life for a thousand miles round ; but it is not so, most of the species 

 are at home, they are indigenous : one-tenth may be strangers ; and some of these are in the 

 colonies, and appear to have come from opposite quarters, i. e. from the north-east and south-west, 

 and at different times. The most crowded parishes, according to our present information, are 

 those of Lochkov and Kozorz. They are neighbours, and may extend over the space of four to six 

 square miles. Of course the strata are only exposed to view in patches, so that we have no access to 

 many of the contained organic remains. 



Within about ten miles from the city of Prague, very nearly the whole series of beds belonging to 

 the Silurian epoch are, at one place or other, largely and clearly brought into view, some few 

 being removed from the top of stage H. In many parishes, such as Hlubocep, Konieprus, Dvoretz, 

 &c., the several stages are seen in their proper stratigraphical relations, while in most other 

 countries hundreds of miles must be traversed in order to see such a succession of fine exposures. 



The following lines give a numerical abstract of all the Bohemian life, as at present determined, 

 with sufficient accuracy. 



This brief account of the leading features of this basin I have ventured to give by way of 

 immediate assistance to the student in what now follows. It may be all had more at large in the 

 works of Barrande and of Murchison. 



On the Place of first Appearance of Bohemian Mollusks. All Silurian life is divisible into 

 the indigenous or native} d the derived or foreign, while every order has some species so 

 ubiquitous that they may be called universals (see p. xxxiii). 



The first class we have seen to be exceedingly numerous ; and the second, although very much 

 fewer, present many points of interest. It is useful to distinguish the indigenous animal from the 

 guest ; it enables us to study the conditions appropriate and natural to all Mollusca that is, the 

 sediments, food, depth, temperature, &c. Curious and instructive particulars also arise in basins 

 from the presence or absence of a tendency there to migrate. 



At this moment I know of 202 Bohemian species which occur in other countries ; there are 

 doubtless many more. Of these 202 species, three-quarters (149) inhabit several horizons, while 

 51 of the remainder, wherever they are met with, are typical of only one horizon. I proceed to 



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