1846.] MURCHISON ON THE SILURIAN ROCKS 'O^^WtebiEN. 41- 



great coral reefs and masses of limestone should be found on the 

 parallel of Wenlock and Dudley — that a band of limestone with 

 Pentamerus IcEvis should turn up in Scandinavia, Russia, and even 

 in America, at precisely the same horizon as the little band of 

 Horderly and Woolhope in England — and that copious lower lime- 

 stones should represent those courses which at Llandeilo and other 

 parts of England and Wales are interpolated in the schists, 

 sandstones and slaty rocks of Britain. 



In speaking of the lithological characters of these lower rocks, 

 Professor Sedgwick further expresses his belief, that " as a general 

 rule, all limestone bands below the carboniferous series are mere 

 local phaenomena appearing at intervals, which are perfectly irregu- 

 lar in countries remote from one another. This remark is meant to 

 include Devonian limestone, and all Silurian limestone both upper 

 and lower *." But this observation is surely as applicable to the 

 limestones above the carboniferous. There are essential distinctions 

 between the strata of the Permian age in Russia and those of West- 

 ern Europe. The dark lias shale of our countries is a solid, light- 

 coloured limestone in the Alps and Carpathians. The middle and 

 lower oolites of the south of England are represented by sandstones 

 and shales in Yorkshire. Even the white chalk, which is the most 

 persistent perhaps of all the secondary deposits of Western Europe, 

 assumes an arenaceous and quartzose type in Eastern Germany, 

 and is unknown in the cretaceous strata of America and Hindostan. 

 Again, if we ascend into the tertiary series, we find the dense 

 clay of London represented by a white shelly limestone at Paris, 

 and the blue marls and sands of the sub- Apennines, the north of 

 Italy, and the basin of the Danube, become fine oolitic limestones 

 in Lower Styria. Having examined a very large portion of Europe, 

 I contend, that there are no secondary, and certainly no tertiary 

 limestones which exhibit a greater persistency when followed to 

 distant tracts, than the limestone of Wenlock and Dudley as de- 

 veloped in the islands of the Baltic, at a distance of near 1000 miles 

 from the typical English formation. Hence I maintain that the 

 original grouping of the strata by reference to such typical limestones, 

 is a better principle of classification than one founded on the slaty 

 and argillaceous constitution of strata of the same age in other 

 British districts since referred to. 



In the same memoir in which the changes or modifications are 

 suggested which have thus led me to express my opinion on the 

 subject, Professor Sedgwick states, that near Builth the lower flag- 

 stones there visible, which contain the Asaphus Buchii, lie a very 

 little below the Wenlock shale. 



If from mentioning this circumstance (which is indicated in my 

 original sections) the object be to infer that the Caradoc sandstone 

 is not a constant stratum between the Wenlock shale and the 

 Llandeilo flags, it is merely the re-announcement of a fact which I 

 have not only long ago admitted, but which I wish to be generally 

 understood. I have indeed specially shown, at first in the year 



* Quart. Geol. Journ. Vol. ii. p. 127. 



