302 NOTES. 



undertaken at my request by Mr C. Peach, have elicited mucl 

 more numerous and more perfect fossils than were previously 

 known ; and these enable me to re-affirm unhesitatingly, that 

 the quartz rocks and limestones of the North-West Highlands 

 are truly of Lower Silurian age. 



" The most striking ot these fossils is the Maclurea, — a 

 genus which as yet has alone been found in deposits of that 

 age. One species was, indeed, figuied in the first edition of 

 this work, and has already been alluded to as occurring in 

 the south of Scotland; but the Sutherland form being unde- 

 scribed, will justly receive the name of Af. Peachii. 



*' The other organic remains belong to the genera Ophile- 

 ta, Oncoceras, and Orthoceras, with small gasteropoda, anne- 

 lides, &c. These shells are all closely allied to (one of them 

 identical with) North American species, so well described by 

 Mr James Hall. In short, they represent the fauna of the 

 Lower Silurian rocks of Canada and the United States, from 

 above the Potsdam sandstone to the Trenton (Llandeilo) 

 limestone inclusive. Let us also observe, that the Scottish 

 and American groupes resemble each other to a great ex- 

 tent in mineral composition, as well as in their fossil con- 

 tents." 



(In order to see this subject still farther explained, and 

 the fossils figured, see the latest edition of " Siluria," pp. 182 

 and 217.) 



Note B, p. 4. 



{From Sir Roderick MurchisorC s " Siluria" p. 284.) 



" It has been shown (p. 153 et seq.) that along the frontier 

 of the Silurian rocks in Shropshire and Herefordshire, where 

 a true mineral transition is seen to take place between the 

 Upper Ludlow rock and the base of the Old Ped Sand- 



