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MIDDLE DISTRICT OF SCOTLAND, 621 



Mineralogists, in general, distinguish two red 

 sandstone formations ; one, the oldest, rests imme- 

 diately on transition or primitive rocks ; the other, 

 and newer, rests on beds of magnesian limestone, 

 coal, and mountain limestone, which are super- 

 imposed on the oldest formation. The mountain 

 limestone, in a general view, may be considered 

 as a transition limestone, contained in the lower 

 part of the red sandstone formation, and bearing 

 the same relation to it, that the beds of red sand- 

 stone in the upper part of the transition series do 

 to grey-wacke. The coal and magnesian limestone 

 are frequently wanting, and then the two red 

 sandstone formations come to rest upon each other. 

 When the sandstone formations are thus arranged, 

 it is difficult to distinguish the one from the other. 

 It may be that they are both only portions of the 

 same great red sandstone formation, and that the 

 coal and magnesian limestone are but subordinate 

 members, that may or may not occur in it, with- 

 out affecting the general characters of the depo- 

 sit as a great formation in the series of mountain 

 rocks. In illustration of this conjecture, it may be 

 stated, that in some extensive red sandstone di- 



alluvial tracts, but also in rocky and mountainous situations, 

 where they flow through valleys, or expand into lakes. These 

 terraces, whether they appear on the banks of lakes, or high up 

 on the sides of valleys, or in low alluvial flats, are to be viewed 

 SIS the effects of water seeking a lower lev^l, whether suddenly 

 •r slowly. 



