412 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 1, 



which well merits a careful examination. I am not aware that 

 any geologists, except Hugh Miller and Dr. Malcolmson, ever visited 

 it* ; and they were not able to detect any fossils ia the sandstone of 

 such great thickness, all of which, however, they clearly recognized 

 to be (as indeed I had ascertained it to be many years before) 

 younger than the Caithness flags. Though much affected by vertical 

 fissures, the beds of the overlying sandstone are clearly seen to be 

 very gently inclined to the N. and N.N.E., in conformity with the 

 underlying flagstones. 



The mere fact that sandstones of such great thickness overlie and 

 graduate downwards into the Caithness flags, has necessarily had 

 great influence in predisposing me to believe that other sandstones, 

 apparently occupying a like position on the south side of the Moray 

 Firth, are also of the Old Red age. This point will be considered in 

 the following memoir. 



On disembarking on ISTorth E-onaldsha, the northernmost of the 

 Orkney Islands, we found that the flagstone series was still persist- 

 ent ; and, though we detected no fishes in our cursory examination, 

 we found there a few fossil plants similar to those of Caithness. 



Judging from the uniform character of the cliffs which we con- 

 stantly passed near to in other islands, such as Rowsha, Stronsha, 

 Shapinsha, and Eda, I infer that the chief stony masses of all the 

 islands, seldom rising to more than 200 feet, are referable to the 

 Caithness flags, though it is probable that the fine building-stones 

 of the two last-mentioned islands, which are of light-yellow and 

 whitish colours, belong to the upper member of the series, or that 

 which we examined in Dunnet Head. 



On the whole, however, and judging from the hard and sUiceous 

 nature of the beds at North E-onaldsha, it would appear that the 

 iehthyolitic and bituminous schists and flagstones, which have their 

 maximum development in Caithness, Pomona, and the Southern 

 Orkneys, part with many of their peculiar characters in their range 

 northwards, just as I have already shown that they change in their 

 eastward range into the north-eastern parts of Sutherland, between 

 Reay and Sutherland. In the sequel, this change of petrographical 

 composition will be still more dwelt upon when we follow these 

 beds southwards into E-oss-shire, and thence to the south side of the 

 Moray Eirth. 



Old Red Sandstone of the Shetland Islands. — In the rapid glance 

 I obtaiued of this extensive group of islands, I could attempt little 

 more than the simple determination that the sandstones, long ago 

 described by Dr. Hibbert as " transition " and " secondary," were 

 prolongations of the Old Red series of the Orkney Islands f. 



At Somburgh Head, the most southerly point of the main island 

 jutting out between the indentations called the East and West Yoe, is 

 a noble vertical cliff 300 feet high, on the summit of which the 



* It appears, from the preceding memoir, that Dr. Malcolmson examined this 

 bold headland in some detail, but met with no fossils there (p. 351 ). 

 t They are now so marked in the Greological Maps of Knipe and Nicol. 



