136 Silurian and Devonian Roch 



so that the series, though with some faults and flexures, is on the 

 whole descending, and exhibits in succession to the rocks just 

 mentioned, gray and dark shales, with bands and lenticular patches 

 of coarse limestone, some of which appear to consist principally 

 of brachiopodous shells in situ, while others present a confused 

 mass of drifted fossils. Below these the beds become more argil- 

 laceous, and in places have assumed a slaty structure, and occasion- 

 ally a red colour. The thickness of the whole series to this point 

 was estimated at 500 feet. The dip then returns to the south, and 

 the beds run nearly in the strike of the shore for some distance, 

 when they become discoloured and ochraceous, and then red and 

 hardened ; and finally, at Arisaig pier, are changed into a coarse 

 reddish banded jasper, where they come into contact with a great 

 dyke of augitic trap of carboniferous date. Beyond this place they 

 are much disturbed, and so far as I could ascertain, destitute of 

 fossils. The alteration of the beds extends to a distance of 300 

 yards from the trap, and beyond this in some places slaty cleav- 

 age and reddish colours have been produced ; the latter change 

 appearing to be connected with vertical fissures traversing the 

 beds. 



In the lower or shaly portion of the Arisaig series, the charao- 

 terstic fossils are GraptoUthus not distinguishable from G. clinto- 

 nensis, Leptoccelia (Atri/pa) intermedia, (Hall,) a new species 

 closely allied to L. hemispherica of the Clinton group of New 

 York, Atrypa emacerata, Orthis testudinaria, Strophomena 

 profunda, S. rugosa, Rhynconella equiradiata, Avicula ema- 

 cerata, TentacuUtes, allied to or identical with T. distans, Helo- 

 j^ora allied to H. fragills. There are also abundant joints and 

 stems of crinoids, and a Palceaster, the only one as yet found in 

 Nova Scotia, which was presented to me by Mr. Honeyman, and 

 has been described by Mr. Billings in the Canadian Naturalist un- 

 der the name of P. parviusculus. These and other fossils associat- 

 ed with them, in the opinion of Prof. Hall, fix the Geological 

 position of these rocks as that of the Clinton group, the upper 

 Llandovery of Murchison, at the base of the upper Silurian or 

 top of the middle Silurian. 



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

 very abundant, and include species of Calymene, Dalmanites, 

 Homalonotus, Orthoceras, Murchisonia, CUdopliorus, TelUnomya, 

 and several brachiopods, among which are Discina tenuilamellata^ 

 Lingula ohlongaj Rhynconella quadricosta, R. Saffordij (Hall,) 



