

GARVH ISLAND. GEOLOGV. 513 



orthoceratites or some analogous fossil, possibly entire 

 shells. On minute examination they prove to be cavities 

 filled with a fine and loose powder of silica; the calcareous 

 matter of the fossil having, as in the case of other silicated 

 remains, disappeared, or possibly entered into some com- 

 bination with the inclosing rock. The analogy of this 

 series to that of the secondary sandstones alternating with 

 limestone, in which organic remains also occur, must be 

 obvious. There is little doubt that a more minute research 

 would discover the same, or perhaps other fossils, in the 

 calcareous beds also ; but the nature of the country, and 

 the position of the rocks, are such as to prevent any 

 minute and profound investigation of this nature in a 

 cursory visit. Whether these shall be discovered or not, 

 it may be concluded that this orthoceratite, if such it 

 be esteemed, is the most ancient organic fossil yet found ; 

 since the relative antiquity of this gneiss can admit of 

 no doubt ; it being a part of the great mass which forms 

 the chief portion of the Highlands of Scotland, from 

 Morven to Cape Wrath on the one hand, and to Cairn 

 gorm and Inverness on the other. 



It is thus consequently proved, that a member of a 

 calcareous series, alternating with gneiss and succeeded 

 by a vast body of that substance, contains organic re- 

 mains ; a character hitherto supposed to be limited to 

 those strata, at furthest, of dubious relative date, which 

 have been called transition strata. It will perhaps con- 

 firm this view to add, that in similar* situations in Assynt, 

 bituminous limestone occurs ; the inflammable matter in 

 this rock being with great reason supposed to have de- 

 rived its origin from organized bodies. 



The existence of organic remains among rocks not 

 appertaining to the secondary class, however compara- 

 tively rare, is sufficiently common to prevent that cir- 

 cumstance from being made a criterion for distinguish- 

 ing them from the primary. The well known expedient 

 of a transition class has been adopted for the purpose 



VOL. II. L L 



