394 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Dec. 1, 



o 



00 

 CM 





03 



o 







I 



O 





2Q 



Cb 



C55 



>1 to 



o2 



§1 



M 



'^ 



f^ 



O.^ 



<5> 



«3H « 



Caithness are not the lower members of the 

 Old Eed Series, as previously stated in geo- 

 logical works. 



The Old Red Sandstone, in the extended 

 sense of the term, is not what some geolo- 

 gists, who have never examined the IN'orth- 

 east of Scotland and the Orkney Islands, have 

 considered it, a small and unimportant for- 

 mation, the upper part of which might be 

 classed with the Carboniferous deposits, and 

 the rest as of no greater importance as to the 

 time occupied in its formation than a mere 

 fragment of the Devonian group only. On 

 the contrary, the Old E-ed group of this 

 northern region is a grand and expanded 

 series of very diversified mineral character, 

 which, both from dimensions and organic re- 

 mains, must be considered a full and adequate 

 equivalent of all the Devonian rocks of South 

 Britain, Germany, Eussia, Prance, Spain, and 

 Tiu'key. The group as seen in Caithness and 

 the Orkney Islands is composed of three 

 parts — 



1. Lower red conglomerate and sandstones. 



2. Grey and dark- coloured flagstones and 



schists, in parts both bituminous and 

 calcareous. 



3. Upper red and yellow sandstones. 



The annexed general section (fig. 9) ex- 

 hibits this order. 



Lower Old Red. — The lower red conglome- 

 rate and sandstone (a, h, c) form the external 

 and unconformable eastern frmge of all the 

 stratified crystalline rocks which have been 

 described. Whether the latter consist of 

 quartzose gneiss at Strathy Head on the north 

 shore, or be followed inland along an irregular 

 boundary by Ben Ghream until they become 

 the thin-bedded quartz-rocks of the Scarabin 

 Hills, or consist of granite at the Ord of 

 Caithness, or of gneissose micaceous schists as 

 they range from Sutherland into Eoss-shire 

 and there occupy the heights of Wyvis or 

 fold round the lower country of Easter Eoss 

 by Dingwall, Brahan Castle, and Fairburn 

 Tower, until they enter Inverness-shire above 

 Beauley, we see everywhere similar rock-rela- 

 tions. Throughout all this tortuous line, the 

 lowest member of the great group under 

 consideration is compounded out of the con- 



