ALTERED LIMESTONE OF STRATH, SKTE. 



69 



opposite side of the Loch the quartzite expands into the broad mass 

 which forms the range of the Sgiath-bheinn hills around Ord, and 

 encloses the well-known limestone basin of that locality. I lately 

 revisited these Ord limestones and at once recognized their identity 

 with the limestones of the interior of Strath. On the western flank 

 of Sgiath-bheiun an Uird I likewise found the yellow dolomitic 

 " fucoid beds " which form so distinct and persistent a member of 

 the Lower Silurian series of Sutherland and Eoss, lying between 

 the top of the quartzite and the base of the limestone. I have not 

 yet succeeded in detecting these easily recognizable beds in Strath, 

 but they will most probably be found there. In the meantime I 

 submit that the stratigraphy of the Strath limestone removes it 

 from the surrounding Lias with which it has been confounded, and 

 places it in the Lower Silurian series of the north-west of Scotland. 



§ 3. Pal^ontological Relations oe the Limestone. 



Though the true position of the massive limestone of Strath was 

 now, in my opinion, established beyond doubt, I was desirous, if 

 possible, to obtain the convincing testimony of organic remains. 

 Eecent experience of the Sutherland limestone led me to hope that 

 among the less crystalline portions of the Skye rock fossils would be 

 found. I accordingly searched the flanks of Beinn Suardal, where 

 the largest area of limestone occurs free from intrusions of " sye- 

 nite." In a preliminary visit I was accompanied by Mr. H. M. 

 Cadell, of the Geological Survey of Scotland, who was fortunate 

 enough to find the first recognizable fossil. Subsequently I spent 

 some time in a more careful examination, and obtained a sufficiently 

 large number of species for purposes of adequate comparison. 



The fossils can hardly be said to be abundant. They occur only 

 in certain dark leaden-grey beds, from the weathered surface of 

 which they project in relief. On a fresh fracture no organic 

 structure is recognizable, but the substance of the fossils is seen to 

 consist of a whiter and more distinctly crystalline calcite. In these 

 respects the Skye rock is precisely the counterpart of some of the 

 beds of the Durness limestone. The subjoined list of species 

 obtained from both sides of Beinn Suardal is sufficient to demonstrate 

 the identity of the horizon of the limestones in these two distant 

 localities, and thus to prove that the altered limestone of Strath is 

 not Lias but Lower Silurian. 



List of Fossils from the Limestone of Beinn Suardal, Strath *. 



Cyclonema. sp. Orthoceras mendax, Salt. (O. vertebrata, 



Murcbisonia, sp. Salt.). 



Maclurea Peachii (?), Salt. baculoides (?), Blake. 



or Ophileta, sp. sp. 



Gasteropod, undeterminable. Piloceras invaginatum, Salt. 



Sponge-like bodies (? Piloceras). 



Annelide-burrows. 



* Compared with the collection of Durness fossils in the Geological-Survey 

 collection, Jermyn Street, and determined by Mr, George Shai-man. 



