184-7 ] MURCHISON ON THE SILURIAN ROCKS OF N. WALES, ETC. 177 



beg to be permitted, without further reference to Russia and Scan- 

 dinavia, to show 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 fossi- 

 liferous rocks of Germany, like those of Devon and Cornwall, are, it 

 is now 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 origi- 

 nal work, the ' Silurian System,' M. Barrande, after collecting 600 

 species of Bohemian fossils, 129 of which species are Trilobites, 

 has, of his own accord, come to the conclusion, that the whole clearly 

 indicate a true Silurian series. The lower half of this series is com- 

 posed 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 sand- 

 stone. The upper group, eminently calcareous, presents itself in three 

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

 nation of the fossils) compares with the Wenlock limestone and shale, 

 fhe 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 different 

 conditions of mineral origin present much fewer points of resemblance 

 to the types of the Silurian region than the above-mentioned distant 

 foreign regions f. 



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

 only. For if it be granted that in Britain the Lower can generally 

 be so separated from the Upper Silurian as to be capable of demarca- 

 tion on a map, how could the geologist succeed in separating the 

 Upper and Lower Silurian of Christiania in Norway, where these 

 groups, each equally well characterized by fossils as in our own coun- 

 try, fold over together in such small united masses j: ? 



* 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 the rock masses in the two 

 countries coincide, and that in Ireland as in Bohemia, the Upper Silurian is emi- 

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

 fossils of Ireland 4to., as published by Mr. Griffith and Mr. M'Coy.) — 9 April 1847. 



X See woodcut, Russia in Europe, &c. vol. i. p. 17, and Quarterly Journal Geol. 

 Society, vol. ii. part 2 (MiscelL), p. 71. 



