THE HELMSDALE STRATA. 435 



the south basin, we find beds of a later age than any of 

 those in the Helmsdale one. I have been unable to trace 

 them continuously, as the shore is much covered towards 

 the centre and south-western side of this passage by 

 sand and shale. The north-eastern side of the Brora 

 basin is equally obscured, and so I cannot regard myself 

 as acquainted with the deposits in succession from 

 Helmsdale to Brora. I think, however, there is evidence 

 that in the Helmsdale basin we have the base of the 

 system, that there is evidence that, in the south 

 basin we have the same base overlaid to a considerable 

 thickness by higher and newer deposits, overlaid by 

 deposits still higher and newer till we ultimately reach, 

 in the bed of white stone of which the additions to 

 Dunrobin Castle have been built, the uppermost deposit 

 of the Oolite on the east coast of Scotland. But though 

 the upper bed occupies a curiously insulated position, 

 the effect apparently of extensive denudation, it lies, so 

 far as I can judge, conformably to the other rocks of the 

 basin. Sir Roderick Murchison, with whose elaborate 

 and valuable paper on the Sutherland Oolite your Grace 

 must be familiar, holds that some of the Navidale 

 conglomerates were formed by the upheaval of the 

 granite of the Ord in a period posterior to the formation 

 of all the Oolites, but it must be a very local conglom- 

 erate that has been so formed, and not the conglom- 

 erate of Old Red Sandstone materials that alternates 

 with the shale beds. 



'I have detected fossil wood in the conglomerate, 

 though not so frequently as coral. Three years ago I 

 saw a piece of wood projecting from a conglomerate 

 cliff immediately above the harbour at Navidale, and it 

 may be there still. Fossil trees were at one time very 

 abundant in the shale beds on both sides of the little 



