188 ProceediTigs of the Royal Physical Society. 



appear to the writer to be due to the reducing action of 

 decomposing organic matter upon solutions of sulphate of 

 lime, partially concentrated in areas temporarily shut off from 

 the sea. In all cases they seem to be simply precipitates, 

 some of which have remained where they were first thrown 

 down; others have formed thin crusts, which have sub- 

 sequently been broken up and redeposited. Most of 

 them are contemporaneous with the formation of the 

 stratum in which they now occur ; while others appear to 

 be due to secondary concretionary action. The whole series 

 is of considerable interest, as marking a transition period 

 between the arid climatal conditions of the Devonian Period 

 and the humid climate of Carboniferous times. 



The second horizon where these curious nodular lime- 

 stones occur, is that of the Eheetic Beds, which bear exactly 

 the same relation to the New Eed below and the Jurassic 

 Eocks above that^ the Cornstone Beds do to the Upper 

 Old Eed and the Carboniferous. Fine sections of these 

 beds are exposed on the west coast of Mull, at Gribun, as 

 well as in the adjacent island of Inch Kenneth. Beds of 

 exactly the same nature occur in Elgin, at Bishopsmill, 

 and other places near Lossiemouth. In all of these the 

 Ehaetic Cornstone Beds are excellently shown. 



Lastly, the most important of these minerals is represented 

 by Haematite. In connection with this I ^ have followed 

 Mr Hudleston^ in referring most of our British deposits of 

 Haematite to an origin connected with closed bodies of 

 saline water — esx3ecially during the New Eed Period. There 

 seems to be good reason for regarding Haematite, as it 

 occurs in Britain, as practically all of New Eed age; and 

 this is true whether the deposit occurs in beds or in veins ; 

 or even where it simply stains the rocks into which it 

 has been transported. A considerable mass of evidence 

 points to the former existence of the New Eed (and, there- 

 fore, of the Ehsetic and Jurrasic Eocks) over a large part 

 of Scotland and other parts of Britain, over all of which 

 it has left its characteristic vestiges in the form of dolomi- 



1 Trans. Edin. Geol. Soc, vii. p. 213. '■^ Proc. Geol. Assoc, xi. p. 104. 



