SKY. GEOLOGY. RED SANDSTONE. 313 



beds maintaining a regular direction, but with a variable 

 dip, lying under a body of limestone on one side and 

 in contact with a mass of gneiss on the other. This 

 series consists of red argillaceous sandstone in various 

 states of induration, of graywacke and simple argilla- 

 ceous schist, of indurated sandstone or quartz rock of 

 a blue, grey, and brown colour, often containing much 

 felspar, and of common white quartz rock. Among the 

 proofs given of the connexion of the members of this 

 series it must be remembered, that the schist is not 

 found exclusively at the lower part and the red sandstone 

 at the upper, but that they both occur indiscriminately 

 throughout the whole ; a circumstance confirmed by 

 their position in other parts of Sky as well as in some 

 of the adjacent islands. It only remains to inquire in 

 what class this series is to be placed, whether among 

 the primary or secondary rocks. Those who should 

 found their judgment on the uppermost portions, or on 

 previous systematical views, would without hesitation con- 

 sider it as a secondary rock, and as analogous to the red 

 sandstone occurring in the centre of Scotland. As such 

 indeed have the red sandstones of all this coast and of 

 the adjacent islands been hitherto considered. But it has 

 been proved both to alternate with and graduate into 

 gneiss, and to consist of a great number of siliceous 

 and argillaceous strata of different characters, some of 

 which are common quartz rock. Under these circum- 

 stances we are entitled to consider it as a primary rock, 

 it being no argument to the contrary that it is followed 

 in parallel order by the secondary strata. This opinion 

 is confirmed by the nature and position of the corre- 

 sponding sandstone on the neighbouring continental shore, 

 a full account of which will hereafter be given when the 

 Sandstone islands shall come under review. 



It is scarcely necessary in concluding this subject to 

 point out to the reader the great thickness of this mass 

 of strata, as it is sufficiently obvious from inspection of 



