74 Geological Society. 



and now offers lithological, stratigraphical, and palseontological 

 evidence that the altered limestone is not Lias but Lower Silurian. 



In lithological characters the limestone, where not immediately 

 affected by the intrusion of tho eruptive rocks, closely resembles the 

 well-known limestones of the west of Sutherland and Rosshire. It 

 is not more altered than Palaeozoic limestones usually are. It con- 

 tains abundant black chert- concretions and nodules, which project 

 from tho weathered surfaces of the rock exactly as they do at Durness. 

 These cherts do not occur in any of the undoubted Lias limestones 

 of the shore-sections. The limestone lies in beds, which, however, 

 are not nearly so distinct as those of the Lias, and have none of the 

 inte Gratifications of dark sandy shale so conspicuous in the true 

 Liassic series. 



The stratigraphy of the altered limestone likewise marks it off from 

 the Lias. There appears to be a lower group of dark limestones full of 

 black cherts, and a higher group of white limestones with little or 

 no chert, which may be compared with the two lower groups of the 

 Durness Limestone. A further point of connexion between the rocks 

 of the two localities is the occurrence of white quartzite in associa- 

 tion with the limestone at several places in Strath, and of represen- 

 tatives of the well-known " fucoid beds " at Ord, in Sleat. These 

 latter strata form a persistent band between the base of the lime- 

 stone and the top of the quartzite, which may be traced all the way 

 from the extreme north of Sutherland southward into Skye. 



Palseontological evidence confirms and completes the proof that 

 the limestone is of Lower Silurian age. The Author has obtained 

 from the limestone of Ben Suardal, near Broadford, a number of 

 fossils which are specifically identical with those in the Durness 

 Limestone, and so closely resemble them in lithological aspect that 

 the whole might be believed to have come from the same crag. 

 Among the fossils are species of Cyclonema, Murchisonia, Maclurea, 

 Orthoceras, and Piloceras. 



The relations of the limestones containing these fossils to the 

 other rocks were traced by the Author. He showed that the Lias 

 rests upon the Silurian limestone with a strong unconformability, 

 and contains at its base a coarse breccia or conglomerate, chiefly 

 composed of pieces of Silurian limestone, with fragments of chert and 

 quartzite. The metamorphism for which Strath has been so long 

 noted is confined to the Silurian limestone, and has been produced 

 by the intrusion of large bosses of granophyre (Macculloch's " sy- 

 enite ") belonging to the younger, or Tortiary series of igneous 

 rocks. 



3. " On the Discovery of Trilobites in the Upper Green (Cam- 

 brian) Slates of the Penrhyn Quarry, Bethscda, near Bangor, North 

 Wales." By Henry Woodward, F.R.S., Y.P.G.S. 



4. " On Thccosponchjlus Daviesi, Seeley, with some Remarks on 

 the Classification of the Dinosauria." By Prof. H. G. Seeley, F.R.S., 

 F.G.S. 



