ROCKS OF THE NORTHERN HIGHLANDS. 359 



(2) Difference of chemical composition. Dr. Heddle quotes ana- 

 lyses of the Assynt and Emboli limestone by Dr. Thomas Anderson, 

 published in the ' Transactions of the Highland Society,' which show 

 that the rock is a " typical dolomite," while the Durness limestone 

 is a "fairly pure" carbonate of lime. I confess myself not fully 

 satisfied with Dr. Heddle's objection. The chemical argument 

 would certainly be of force if it stood alone ; but it would have 

 little weight against the merest fragment of fossil proof. The evi- 

 dence of the orthoceratites. is certainly not decisive; but at the 

 same time I hesitate to reject the testimony of such competent ob- 

 servers as Murchison, Peach, and Salter. That the specimen de- 

 scribed by Salter was truly an orthoceratite no one who is acquainted 

 with the work of that accomplished palaeontologist can reasonably 

 doubt ; and that Mr. Clark palmed a deception upon Murchison is 

 not easy of belief, both from the want of motive and from the diffi- 

 culty of obtaining the specimen. 



But,even waiving the fossil testimony just discussed, there are other 

 facts which militate against the Archaean age of the Assynt series. 

 Foremost amongst jbhese I would place the comparatively unaltered, 

 state of the rocks. The quartzite bears but little upon the point, 

 since we have in the British Islands undoubted quartzites as young 

 as the Llandovery and as old as the Dimetian. But the beds above 

 the quartzite display very slight alteration. In the Brown Flags are 

 shales and slates as unchanged as any of Lower Palaeozoic age 

 (Nos. 103, 104, 107, 108, p. 418). In Assynt the Flags contain 

 abundant vegetable impressions, the carbonaceous matter being as 

 distinct and apparently as unaltered as in coal-shales. The unme- 

 tamorphosed state of these beds cannot be accounted for on any 

 principle of selective metamorphism. The rocks furnish all the 

 materials for the production of schists. Magnesia is provided by 

 dolomitic flags and limestones. Iron is so abundant that it gives 

 the flags their distinctive colour. Alumina and alkalies are sup- 

 plied by argillaceous, felspathic, and micaceous constituents. Yet 

 with all the ingredients at hand, not a seam of true metamorphic 

 rock has been formed. 



It is not here contended that the absence of metamorphism is 

 absolute disproof of great antiquity ; but as all Archaean rocks 

 hitherto studied are more or less metamorphosed, the presumption 

 that an unaltered rock is not Archaean is very strong indeed. 



The abundance of fossil remains is also unfavourable to the 

 Archaean hypothesis. The upper part of the quartzite is full of the 

 well-known " worm-holes." In the same beds are numerous conical 

 bodies, with a cone-in-cone structure. In transverse section, as 

 they appear on the surface of the beds, the fossils are like three 

 concentric rings, the central one being in diameter about g inch, 

 and the outer ring 1 inch. These peculiarities are hardly such as 

 we should expect in Annelids. Besides the above, there are the 

 " Fucoids " of the Brown Flags. Some of these are described by 

 Nicol as "straight, cylindrical fragments, like stems or branches of 

 trees .... Some are marked with obscure scars, as of leaves and 



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