J. W. JTTDD ON THE SECONDARY ROCKS OP SCOTLAND. 685 



tides. Hence the geologist has to wait for a favourable concurrence 

 of suitable low tides with an off-shore wind in order to be able even 

 to approach the object of his quest. 



Small in extent, however, as is this outlying patch, and difficult 

 of access, it fortunately yields to us most unmistakable and satis- 

 factory evidence of its age and characters. I have several times 

 succeeded in reaching the spot when the conditions were favourable 

 for its examination — sometimes by traversing the face of the grand 

 basaltic cliffs of Ardtornish, at other times by means of a boat from 

 Loch Aline or the opposite shore of Mull. During the last season I 

 had the pleasure of visiting the locality in company with Dr. Taylor 

 Smith, during very stormy weather, it is true, but at a time when 

 the other conditions were particularly favourable for the study of the 

 rocks. 



These beds of the Innimore of Ardtornish consist of somewhat 

 coarse white sandstones, and of fine-grained highly micaceous sand- 

 stones of a very dark tint, passing occasionally into shales. Both 

 the coarse-grained and the fine-grained rocks are crowded with 

 plant-remains, which in the former exist as hollow casts, and in the 

 latter retain their carbonaceous matter. Occasional thin and imper- 

 fect seams of coal occur, and the agreement in physical characters 

 of this most northern patch of Carboniferous strata with the strata 

 of the same age in other parts of our islands is most complete and 

 striking. 



Fortunately, too, the palseontological evidence as to their position 

 in the geological series is of the most satisfactory character. The 

 plant-remains, though abundant, are seldom sufficiently well pre- 

 served for specific determination. Among the forms which I have 

 been able to detect as occurring there are : — 



Lepidodendron aculeatum, Presl. 

 Catamites Suckowii, Brongn. 

 Cistii, Brongn. 



Sigillaria Saullii, Brongn, 

 Stigmaria. 



The only specimen of Lepidodendron which I have been able to 

 obtain is an example more than a foot in diameter. This and the 

 species of Calamites afforded the most satisfactory evidence concerning 

 the age of the strata. 



I may add that my recognition of the age of these deposits is sup- 

 ported by the opinion of the most competent palaaophytologists from 

 the examination of the specimens obtained. Sir Charles Bunbury, 

 to whom my earliest specimens were sent by the late Sir Charles 

 Lyell, and Mr. Carruthers and Professor Morris, who have examined 

 a somewhat larger series, all agree that it is impossible to refer the 

 plant-remains to any other horizon than the Carboniferous. 



This series of Carboniferous strata, where best exposed, cannot 

 exceed 40 or 50 feet in thickness ; its relations, however, are unfor- 

 tunately by no means very clearly exhibited. That it reposes directly 

 upon the gneissic rocks of the district there is every reason for be- 

 lieving ; for these rocks compose the islands of Eidire and the Grey- 

 Island group, which rise above the waters of the Sound of Mull be- 



