SILURIAN. 261 



Division 3. — In this division there are 53 species, of which 23 are received from division 1, 

 and 26 pass upward. We here meet for the first time with Pentamerus ohlongus, Stricklandinia 

 lens, S. lirata, S. hrevis, and Laptoccelia hemispTierica. These are aU strongly characteristic of 

 the Middle Silurian and occur in this division and also in division 4 in great abundance. 



Division 4- — There are 70 species from this division, of which 26 are received from below. 



CONCLUSION. 



The great abundance of such species as Strophomena rhomboidalis, S. pecten, S. antiquata, 

 Leptsena transversalis, Orihis davidsoni, Pentamerus ohlongus, StricMandinia lens, S. lirata, S. hrevis, 

 Gyrtia myrtea, Spirifer plicatella, and Leptocoelia TiemispJierica, together with the general aspect 

 of the whole fauna of divisions 3 and 4, render it quite certain that this part of the series repre- 

 sents the Upper Llandovery rocks of England and, perhaps, the Lower Llandovery also. They 

 may not be exactly synchronous, for it seems to be now pretty conclusively demonstrated that 

 a fauna may appear somewhat earlier in one region than in another. But, so far as we can at 

 present decide the question by fossil evidence, these rocks are of the same age. I use the word 

 fauna in a purely zoological sense, with no reference to geographical distribution. With regard 

 to the Llandovery formation, Mr. Salter "^ makes the following remarks: " The Lower Llando- 

 very, or, as I prefer to caU it, with Prof. Phillips, the Llandovery rocks, are intimately \mited 

 with the Caradoc, and pass up from them with a great admixture of Lower Silurian, not Upper 

 Silurian, forms. The May HiU sandstone, on the contrary, as Sedgwick showed in 1853, is 

 unequivocally the base of the Upper Silurian, and contains scarcely any true Lower types." 

 Now, the only deposit, as yet known in America, which exhibits such an admixture, is division 1 

 of the Anticosti group. If, then", the extinction of the Lower Silurian fauna occurred in the 

 ancient British seas at the same time that it did in the American waters, it follows that division 1 

 is Lower Llandovery; and that the Hudson River is Caradoc. 



It is, however, very difficult to correlate all the divisions of the English Middle and Lower 

 Silurian with those of America, and I shall take tliis occasion to make a few observations on the 

 other members of the series not found in Anticosti. From what we know of the origin and mode 

 of accumulation of sedimentary strata, it is highly improbable that each of the minor formations 

 of one country should have its exact equivalent in anotiier land several thousands of miles away, 

 although the larger groups, of which these smaller ones are the component parts, may be well 

 represented, and paralleled in a general way. Everywhere we find a number of breaks or gaps, 

 and the probabihties are vastly against these breaks having been all occasioned at the same time 

 in distant locahties. It is more consistent with the nature of tilings that many of the breaks 

 in Ainerica should stand opposite — so to speak — tlie formations in England, and vice versa. 

 Perfect parallelism of the minor groups may be looked for as the exception, not the rule.'' 



M-N 13-14. LAKE WINNIPEG, MANITOBA, AND SASKATCHEWAN; 



The Silurian of northwestern Manitoba is a thin-bedded limestone, which varies 

 in character from bed to bed. The lower portion, well exposed at Grand Rapids, 



" Geol. Mag., vol. 3, p. 240. 



6 Prof. A. C. Ramsey (Anniversary address to the Geological Society, 1863: Jour. Geol. Soc, vol. 19) gives the 

 following account of the breaks in the English series from the Lingula flags up to the Wenlock shale; 

 Lingula flags. 



Break very nearly complete both in genera and species, and probable unconformity. 

 Tremadoc slate. 



Break very nearly complete, both in genera and species, and probable unconformity. 

 Llandeilo and Caradoc beds. 



Large break, especially in species, and probable unconformity. 

 Lower Llandovery beds. 



Break and decided unconformity. 

 Upper Llandovery beds. 



Break and strong unconformity. 

 Wenlock shale, etc. 



