HOISEYMAN GEOLOGY OF ANTIGONISH COUNTY. 109 



amination of the equivalency of the Arisaig group, as the graptolites 

 of B appear to have the facies of the graptolites of the Hudson River 

 group, so that a and B may be the Arisaig equivalent of this group. 

 Instead therefore of beginning with the upper Silurian age, it may 

 begin with part of the lower silurian, so that in Arisaig 



A and B are probably equivalent to the Hudson River Group 

 — Lower Silurian 

 B = the Clinton, ^ 



C = the Niagara Limestone, > Upper Silurian. 

 D = the Lower Helderberg, ) 

 It may be interesting to observe that graptolite life in Kova 

 Scotia appears to range higher than in the LTnited States, as accord- 

 ing to Hall and Dana, Graptolithus Clintonensis existed alone there^ 

 and was the last of its race. Mobile with us Graptolith'us Clintonensis 

 is associated with several other monoprionideans, and in 1864 I 

 found in c, associated with crinoids, in shale interbedded among 

 strata containing noble cephalopoda, a diprionidean graptolite of sin- 

 gular size and form. This graptolite is being examined by Prof. 

 Wyville Thomson, and is to be described and figured in his work on 

 Graptolites. Since I wrote the paper on the Geology of Arisaig 

 referred to, 1 have had occasion to make a more particular examina- 

 tion than I had before made of the junction of the silurian with the 

 carboniferous, at McAra's brook, and I am led to believe, by com- 

 parison with other localities, especially with Lochaber, which we 

 shall shortly examine, that the apparent uncomformability is not real, 

 and that the strata exposed on the shore and up the brook, are a 

 formation intermediate between D, the equivalent of the upper 

 Ludlow or lower Llelderberg, and the lower carboniferous that 

 forms the adjacent mountain west of the brook, in other "words that 

 the strata in question are Devonian. From these observations it 

 would appear that in Arisaig we have a series ascending from the 

 Hudson River age into the lower carboniferous, without any break 

 in succession. These observations tend to modify the opinion ex- 

 pressed by Prof. Leslie, quoted by Dr. Bigsby in his paper read 

 before the Geological Society — " On Missing Sedimentary Forma- 

 tions." It appears from this that Prof. Leslie is of opinion that the 

 lower carboniferous at Arisaig lies unconformably on the Clinton 

 equivalent. At Lochaber lake^ which was mentioned in an introduc- 

 14 



