1846.] MURCHISON ON THE SILURIAN ROCKS OF SWEDEN. 4-3 



than that which was afforded in the work which established the 

 Silurian system. We there find, that out of the twenty-five species 

 of Orthidae (including in that number four forms doubtfully referred 

 to Spirifers) one species only, the Orfhis caiialis, had been then 

 observed by myself to pass up into the Wenlock formation ; whilst 

 after years of assiduous labour, Professor Sedgwick and Mr. Salter 

 add but one other species, the Orthis lata, which also rises from 

 the one group into the other. The occurrence of Trinucleus 

 Caractaci in the Wenlock shale, and of Calymene Blumenbachii in 

 the Caradoc sandstone, does not invalidate the fact, that the one 

 crustacean occurs in myriads in the Lower and most rarely in the 

 inferior part only of the Upper, and the other abundantly in the Upper 

 group and very seldom in the higher part of the Lower ; whilst 

 among the thirty-eight species of Trilobites published in the ' Silurian 

 System,' nineteen are still recognised as exclusively Upper Silurian, 

 and fifteen or sixteen as Lower Silurian forms. 



I must also dissent from the plan whereby Professor Sedgwick 

 strengthens his conclusions, by excluding corals from his calcula- 

 tions, " as being too widely spread," for by the valuable labours of 

 my friend Mr. Lonsdale, I have shown (and the demonstration has 

 never been invalidated) that by far the greater number of the 

 Silurian zoophytes are confined to the Upper Silurian, and that 

 whilst eight or nine species only descend into the Lower stage, the 

 latter contains some species which have never yet been detected in 

 the Upper. Nor can Crinoidea be considered too imperfect to be 

 of value in establishing a classification. The beautiful forms of 

 Actinocrinites moniliformis^ Hypanthocrinites decorus, the five species 

 of Cyathocrinites, and other species of the Dudley limestone both 

 published and unpublished (all generally recognised as true Upper 

 Silurian types), have nowhere been found in the Lower Silurian 

 strata, whilst on the contrary in Russia, Scandinavia and Britain, 

 the Cystidea form a typical Lower Silurian group representing the 

 Crinoidea, and not met with in the Upper group. 



But if by such striking evidence, as well as by the absence of 

 yertebrata, the Lower Silurian may generally be well separated from 

 the Upper, 1 am far from denying that among the 500 Silurian 

 species alluded to by Professor Sedgwick, a few (more even than he 

 has mentioned) may not pass from the one group to the other. Since 

 Mr. W. Smith established his succession of the Oolitic series of 

 England, a number of fossils ten times greater, I will venture to 

 say, has been found to be common to his widely-honoured groups, 

 than by the incessant researches of a number of the best geologists 

 in England, in Siluria, and Wales, have been shown to be common 

 to my Upper and Lower groups ; but such a reason has not been 

 deemed sufficient to induce us to change the classification established 

 by the Father of English secondary geology. So far from regretting 

 that multiplied observations subsequent to my own have brought 

 out the fact (which will be rendered more striking when the results 

 of the Geological Survey of Great Britain are published), that a few 

 more species are common to the Lower and Upper Silurian than 



