1873.] * JTTDD THE SECONDARY ROCKS OF SCOTLAND. 131 



to the patches in Ross * ; and Prof. Eamsay informs me that, when 

 he examined the Brora district some years ago, he was led to adopt 

 the same views with regard to it. 



§ 5. Confirmations of the above conclusions concerning the Relations 

 of the Palaeozoic and Mesozoic Strata. 



I have now to point out two very remarkable and interesting 

 phenomena, which, while they are on the one hand altogether ano- 

 malous and inexplicable, except on the hypothesis that the two 

 series of rocks have acquired their present relations through the 

 agency of great faults, are, on the other hand, seen to be in most 

 complete harmony with the inferences to which all the other facts 

 have led us. 



It will be shown hereafter that the Upper Oolite beds in portions 

 of this district are almost wholly made up of derived blocks. These 

 blocks so precisely agree in mineral character with the Caithness 

 Flagstones and associated beds of the Middle Old Red Sandstone, 

 that Sir Roderick Murchison was evidently strongly inclined to refer 

 them to this source. One fact, however, appeared to offer insuper- 

 able difficulties to accepting such a conclusion. The rocks which 

 now appear in closest proximity to the Secondary strata in question 

 are the Ord Granite, and the conglomerates and sandstones of the 

 Lower Old Red, while the Middle Old Red Sandstones were then 

 known only at a considerable distance. Sir Roderick pointed out 

 the remarkable fact, which subsequent observations have completely 

 confirmed, of the total absence of fragments of those well-marked 

 and most easily recognizable rocks (the Ord Granite and the Old 

 Red Conglomerate) in the " brecciated beds " f . 



So fatal did Sir Roderick consider this fact to the hypothesis 

 that the blocks in question were derived from the Palaeozoic strata, 

 that he found himself compelled to abandon it ; but it is with evi- 

 dent doubt and reluctance that he resigns the theory in question in 

 favour of another. 



As I shall have to show more fully hereafter, the fact that these 

 blocks in the " brecciated beds " are derived, and that they are of 

 Middle Old Red Sandstone age, is put out of all question by the 

 discovery in them of the remains of the characteristic fishes. The 

 difficulty pointed out by Sir Roderick Murchison reappears therefore 

 with its full force. 



If, however, we admit that the present position and relations of 

 the Primaiy and Secondary strata are due to a great fault, this 

 startling difficulty at once disappears ; for the thick series of the 

 Middle Old Red Sandstone, so magnificently developed in Caithness, 

 where it has escaped denudation, might then have formed the 

 lands bounding the Oolitic sea, while the granite of the Ord and the 

 conglomerates and sandstones of the Lower Old Red were buried 

 below thousands of feet of newer rocks. 



* Scenery of Scotland, p. 177. 



t Trans. Geol. Soc. 2nd ssr. vol. ii. pt. 2. pp. oOf), 307. 



K 2 



