160 Sir Roderick I. Murchison on the 



Whilst we are considering what are the natural distinctions of a 

 system, or " terrain," in the sense in which I used the word, I beg 

 to be permitted, without further reference to llussia and Scandinavia, 

 to shew how, in another portion of the continent, the Silurian system 

 has recently been applied by a French geologist, M. Barrande, to 

 Bohemia, the country of his adopted residence. The slaty fossilife- 

 rous rocks of Germany, like those of Devon and Cornwall are, it is 

 well known, for the most part of Devonian age ; but in Bohemia, a long 

 and wide tract consists of a basin of Silurian rocks, the lowest strata 

 of which repose on sedimentary rocks void of fossils, and these again 

 on crystalline schists. With no other guide than my original work, 

 the " Silurian System," M. Barrande, after collecting 600 species of 

 Bohemia fossils, 129 of which species are Trilobites, has, of his bwn 

 accord, come to the conclusion, that the whole clearly indicate a true 

 Silurian series. The lower half of this series is composed of two 

 stages of quartzose and argillaceous strata, which are not merely 

 referred to the Lower Silurian as a whole, but, through their mineral 

 characters and their Trilobites, and other organic forms, are even 

 severally compared with the Llandeilo flags and Caradoc sandstone. 

 The upper group, eminently calcareous, presents itself in three 

 stages, the lowest of which M. Barrande (after most assiduous ex- 

 amination of the fossils) compares with the Wenlock limestone and 

 shale, the middle with the Lower Ludlow rock (the chambered shells 

 of which strikingly resemble those of the same formation in England), 

 and the third or upper division with the Aymestry limestone and 

 Upper Ludlow rock. I advert, therefore, with pleasure to such 

 labours, because they prove that the detailed descriptions of certain 

 typical Silurian tracts in England have not been unfruitful, even in 

 reference to other and distant European tracts. I further trust that 

 geologists may regard my late memoir on Gothland as a corrobora- 

 tion quite as striking, of the value of the detailed original description 

 of the types of my own country.* On the other hand, I well know 

 that there are Silurian tracts in the British Isles, which, under dif- 

 ferent conditions of mineral origin present much fewer points of re- 

 semblance to the types of the Silurian region than the above men- 

 tioned distant foreign regions. f 



But rock systems must not be so formed as to suit one country 



* See Quarterly Journal Geol. Soc, vol. iii., p. 1. 



t Whilst these pages are passing through the press, I have learnt from Mr 

 M'Coy, that several of the Upper and Lower Silurian species of Ireland, which 

 he has described and named, are identical with specimens from Bohemia now 

 in the collection of the University of Cambridge ; and together, with this fact, 

 it is curious to remark, that the mineral characters of tlie rock masses in the 

 two countries coincide; and that in Ireland, as in Bohemia, the Upper Silurian 

 is eminently calcareous, the Lower Silurian sandy, quartzose, and slaty. (See 

 the Silurian fossils of Ireland, 4to, as published by Mr Grriffith and Mr M'Coy). 

 — 9«* April 1847. 



