ON THE LIMESTONE OF DURNESS AND ASSYNT. 



239 



16. The Limestone of Durness and Assynt. By C. Callaway, Esq., 

 M.A., D.Sc, F.G.S. (Eead January 5, 1881.) 



It is well known that the late Sir I. Murchison based his deter- 

 mination of the Ordovician (Lower Silurian) age of the greater part 

 of the Scottish highlands upon the discovery hy Mr. C. Peach of 

 Ordovician fossils in the Durness limestone. The views of Mur- 

 chison were shared by many distinguished geologists, and have been 

 generally accepted as one of the most assured and important conclu- 

 sions of modem geological science. Wishing to ascertain for myself 

 the truth of this opinion, I devoted a portion of last summer to the 

 study of the limestone at Durness and Inchnadamff. I selected these 

 localities because they alone are alleged to have yielded fossils from 

 the limestone, and because Murchison regarded them as of primary 

 importance in the construction of his argument. My researches led 

 me to the conclusion, not only that the sections were broken, and 

 therefore untrustworthy, but that the relations of the several rock- 

 groups were inconsistent with the supposition that the limestone 

 passed below any part of the newer metamorphic series. On my 

 return from Sutherland, I found that many of my observations 

 agreed very closely with those of Prof. jSTicol ; and I am glad to 

 bear testimony to the accuracy of an author whose work has hardly 

 received due recognition. It is certain that he made out many im- 

 portant points which escaped the observation of his distinguished 

 rival ; and I must, in candour, acknowledge that he has anticipated 

 many of the results which I have now to submit to the Society. 

 I can only claim to have ascertained some additional facts, which 

 seem to me to strengthen the case against the received opinion. 



Durness. 



a. The Limestone in Relation to the Flaggy Gneiss. — In his later 

 papers, Murchison admitted that the limestone was separated from 

 the flaggy beds * by a " great fault," by which the " upper quartzite " 

 was thrown down out of sight ; but he, notwithstanding, held that 

 the limestone was " overlain by the upper series of quartzose and 

 gneissic rocks," apparently on the ground that both dipped in the 

 same direction, to the east. Admitting his facts, his reasoning is 

 obviously fallacious, and might be employed to prove the most op- 

 posite conclusions. But I cannot accept his facts. Neither the 

 limestone nor the flaggy group dips to the east. The true relations 

 of the two formations are shown in the annexed plan (fig. 1), which 

 is, in outline, a reduced copy of the new ordnance map. The most 

 important dips are shown by arrows. 



* These flags are a true schist, though they are far less coarsely crystalline 

 than the Lewisian. 



