On the Genesis of Some Scottish Minerals. 189 



tised and ferrified limestones of older date, deposits of 

 Haematite (which are almost invariably pseudomorphous 

 after calcareous deposits) and sandstones stained red, which 

 colour gives place to lilac, dull-puce, and purple tints, 

 where the rocks so affected happen to have contained 

 carbonaceous matter. Haematite is practically indestruc- 

 tible; hence the geological value of the evidence afforded 

 by these red stained and ferrified rocks is considerable. 

 Wherever these vestiges of the JSTew Eed occur, there also 

 must have been both the Ehsetic Eocks and also those 

 of a Jurassic age, for in no part of Western Europe did 

 the New Eed occur without these strata succeeding it. 

 I have repeatedly emphasised the significance of these 

 facts, chiefly in relation to the comparatively recent origin 

 of the mountains and valleys of North Britain.^ 



Some deposits of Manganese, and possibly a few of 

 Gcethite and Limonite, may have originated in the same 

 manner as Haematite. 



No hard line can be drawn in every case between the 

 origin of some of these lacustrine deposits and those formed 

 at the bottom of the sea. The two chief Scottish examples 

 of these are Pyrites, whose constituents colour the "blue 

 clays " of Murray and Irvine,^ and the nodular deposits of 

 Manganese described by the same authors.^ 



A 2. The chief Scottish minerals referable to this category 

 have already been noted incidentally. 



A 3. Those due to the subterranean percolation of waters 

 from the surface. 



{a) Those altered in sit4. 

 To this section must be referred a large number of those 

 minerals that have undergone pseudomorphic change by the 

 action of water. In addition to the pseudomorphs, com- 

 monly understood as such, there are the well-known 

 examples of Serpentine and Kaolin, as well as a few others 



1 Trans. Cumb. and West. Assoc, viii. p. 888 ; Trans. Edin. Geol. Soc, 

 vii. ; Trans. Glasgow Geol. Soc, xi.; and other places. 



2 Murray and Irvine, Trans. Roy. Soc Edin,, xxxvii. ' Ibid. 



