xxiv FACTS AND OBSERVATIONS. 



singular interest, and to bring within our view much that is new in the history of Silurian species, 

 their time of appearance, duration, classification, &c. 



The Silurian beds near Prague enjoy a zoological opulence surpassing all previous experience, 

 taking into consideration their very small extent, which bears no kind of comparison with the size 

 of other basins. 



"Within an oval space (mostly on the west of this city) fifty miles long by twenty-five broad, 

 2800 species of marine remains have been collected, and 2093 have been described by M. Barrande. 

 Of course, individuals are in millions incalculable. Four-fifths of this fauna are furnished by 

 the four orders Cephalopoda, Trilobita, Brachiopoda, and Gasteropoda, and chiefly in the small 

 parishes of Lochkov, Kozorz, Butowitz, Konieprus, and Mnienian. 



Further, the conditions of this Silurian area are in discrepancy with some of our established 

 notions. It is a close basin with an immense variety of life a basin with very small foreign 

 interchange. During a short time its gates were opened thrice, and then closed almost totally, and 

 for ever. It abounds, except in its Primordial beds, with powerful Carnivora, the lower forms being 

 very scarce, while its higher strata (H. h. 1) give out two land plants, unhesitatingly pronounced to 

 be such by M. Barrande. The area has been frequently overflowed by thick and by thin sheets of 

 trap and porphyries, from what sources I know not, but without a single marked boss or upheaval 

 of any kind. 



This whole Silurian district is 100 miles by 44 in its greatest dimensions, and is a long oval ; 

 perhaps a third of the size of Wales. 



The accompanying Sketch Map represents about one half of the area, and that which is richest 

 in fossils. 



Easy access is obtained to good sections by means of quarries, ravines, and watercourses. 



The strata repose in synclinal conformableness, zone upon zone, except in a few cases of local 

 derangements, and an occasional change of dip. At the bottom of this succession are M. Barrande' s 

 stages A and B, wholly azoic, principally schists, abutting directly on granite and gneiss. These 

 same schists, as they ascend, at length betray Primordial life, and are then distinguished by the 

 letter C. They are 900 to 1200 feet thick, thin and close-packed on the south-east, but much 

 separated on the north-west by intercalated porphyries and conglomerates. 



The next stage upwards is that of D (56 miles by 9 to 12 miles) . In its lower half it is made 

 up of alternating schists, quartzites, and conglomerates, followed above by very thick beds of 

 coloured schists. This stage has been subdivided thus : 1. At the base, schists with conglomerates. 

 2. The quartzite band of Mount Drabow, with conglomerates both together forming half of the 

 whole stage. 3. Black foliated schists. 4. Very micaceous schists. 5. Yellowish-grey schists, 

 supporting the trappose base of stage E next succeeding. These schists, 3, 4, 5, are 3000 feet 

 thick. Stages C and D contain no limestone. 



In this stage D, in d. 3, 4, 5, are the celebrated colonies, twenty in number (M. Barrande, MS.), 

 lying along a certain zone. Eight have been described (see sketch) . They consist of traps inter- 

 leaved with graptolite schists, holding calcareous concretions, pretty full of organic remains. The 

 presence of these colonies indicates a general but slight disturbance, of which few other signs 

 remain. A great peculiarity in their life is that they are precedent (prophetic of) and not posterior, 

 as recurrents, to the great normal fauna about to appear. 



The stage E (Upper- Silurian) is based upon broken sheets of trap, alternating with graptolite 

 schists. These traps form a true girdle, about 300 feet thick, to the upper stages E, F, G, and H, 

 which correspond in great measure with the Upper Silurian of England and other parts of the 

 world. The stage E, with its trappose base, consists of argillo-calcareous nodules long, flattened 

 spheroids, imbedded in argillaceous schists, which (nodules), the te*p 'disappearing in the ascent, 

 gradually coalesce into compact fetid limestone. The whole stage is 450 to 900 feet thick. 



M. Barrande has separated this stage into two parts, E. e. ] and E. e. 2, both of them 

 singularly abundant in marine life. 



