566 THE UPPER SILURIAN. 



ecelia {Atrypa) intermedia (Hall), a new species closely allied to L. 

 hemispherica of the Clinton group of New York, Atrypa emaceraia, 

 Orthis testudinaria, Strophomena profunda, S. rugosa, Rliynchonella 

 equiradiata, Avicula emaceraia, Tentaculites, allied to or identical with 

 T. distans, Helopora allied to H. fragilis. There are also abundant 

 joints and stems of crinoids, and a Falceaster, the only one as yet 

 found in Nova Scotia, which was presented to me by Dr Honeyman, 

 and has been described by Mr Billings in the "Canadian Naturalist" 

 under the name of P. parviusculus. These and other fossils associ- 

 ated with them, in the opinion of Professor Hall, fix the Geological 

 position of these rocks as that of the Clinton group, the Upper Llan- 

 dovery of Murchison, in the central part of the Upper Silurian. 



In the upper and more calcareous part of the series, fossils are very 

 abundant, and include species of Calymene, Dalmania, Homalonotus, 

 OrthoceraSf Murchisonia, Clidophorus, Tellinomya, and several bra- 

 chiopods, among which are Discina tennuilamellata, Lingula ohlonga, 

 Rhynclwnella quadricosta, R. Sajhrdi (Hall), allied to R. Wilsoni, R. 

 neglecta, Atrypa reticidaris, all found in the Upper Silurian elsewhere 

 in America. Most of the other forms are new species, descriptions 

 of which have been given in Professor Hall's paper. The general 

 assemblage is on the whole not unlike that of the Clinton, but is of 

 such a character as to warrant the belief that we may have in these 

 beds a series somewhat higher in position, and probably equivalent 

 to the Lower Helderberg, the Ludlow of the English geologists. The 

 new species Chonetes Nova-Scotica is very characteristic of the upper 

 member. 



On the whole, we must regard the Arisaig series as representing 

 the middle and upper parts of the Upper Silurian, a position some- 

 what lower than that assigned to it in the first edition of " Acadian 

 Geology." In explanation of this, I may further state that, in papers 

 published previously to 1855, I had regarded these rocks as Silurian; 

 and that it was only in deference to the opinions of able palaeontologists, 

 both in Britain and America, who compared the fossils with those of 

 the Hamilton group, that I abandoned this view, returning to it in 

 1859, when enabled to do so by Professor Hall's examination of the 

 fossils, the results of which were published in 1860. It is only just 

 to Dr Honeyman to state, that he had independently stated similar 

 conclusions in Nova Scotia in 1859. Unfortunately the Arisaig 

 series stands alone, wedged between Carboniferous and Plutonic rocks, 

 so that little opportunity occurs on the coast of verifying the con- 

 clusions derived from fossils, by the evidence of stratigraphical con- 

 nexion with newer or older Silurian deposits, and I have been unable 



