LOWEST, OR OLD RED, SANDSTONE. 219 



upper sandstones. And it is a connected fact, leading 

 to a similar inference, that the indurated beds occur in 

 the vicinity of the primary rocks, and more particu- 

 larly in that of gneiss or the other older strata, as the 

 less compact ones are found in the reverse situations. 

 And of all these argillaceous beds I must remark, that 

 they are commonly so inferior in quantity to the sand* 

 stone that they may be called subordinate, though 

 Orkney produces a notable exception. 



The frequent confusion produced respecting this 

 sandstone, by the adoption of the term Red, obliges 

 me to notice what I have seldom done respecting rocks. 

 It occurs of all hues, from nearly perfect white to dark 

 grey, and also of yellowish tints, independently of its 

 various tones of red ; while it is further often mottled 

 and spotted with red and white, so as to have been 

 thence mistaken for the red marl sandstone, by those 

 to whom the term variegated constituted knowledge. 

 Thns have many of these, especially when incompact, 

 and when occupying large tracts, as they often do, 

 been mistaken for other and superior sandstones; as 

 have the hard kinds, lying near the primary strata, for 

 quartz rock, from which, in detached specimens, they 

 are in reality undistinguishable. I may also repeat, 

 that the hard and grey varieties sometimes become 

 yellow and tender, even to a great depth and extent, 

 by a decomposition in situ., as in Orkney, so as to have 

 led to similar false inferences. L-et the geologist ever 

 remember that it is his business to trace geological 

 connexions before he determines geological characters. 



The last circumstance in the history of this sand- 

 stone, relates to the rocks with which it is contermi- 

 nous, and is necessarily dependent on the number of 

 members in the inferior series, and on the order in 

 which these are placed. The contact with coarse, or 



