30 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 31, 



that this modern deposit is quite analogous to many grey beds of 

 great antiquity, in which sulphuret of iron is mixed with organic 

 matter, and there can be little danger in inferring that the causes in 

 both cases are the same. I may mention, that in some parts of the 

 deposit forming in Pictou harbour, the vegetable matter which has 

 caused the change of colour is so completely decomposed that no 

 visible fragments of it remain. I may also notice in passing, that 

 this mud contains vast numbers of the siliceous coverings of infusoria. 



Another modern cause of change of colour in red sands and clays, 

 is the action of acids produced in the putrefaction and decay of moist 

 vegetable matter. This is the usual cause of the whiteness of the 

 subsoils of peat bogs and swamps, and in such places the oxide of iron 

 is often redeposited at the outlet where surplus water escapes from 

 the bog. This process also probably prevailed extensively in the 

 freshwater deposits of former periods, and may have changed the 

 colours of clays and sands, and have collected their colouring matter 

 in bands and nodules of carbonate and hydrous peroxide of iron. 

 Beds bleached in this way of course do not resume their colour when 

 heated . 



It is evident that the formation of red sediment and its partial 

 decoloration may have frequently alternated in the same locality, or 

 have occurred at the same time in neighbouring localities ; and when 

 viewed in this way, they possess some interest independently of the 

 explanation of the colours of rocks. First, they satisfactorily account 

 for the rarity of fossils in red beds ; since both the red oxide of iron 

 and sulphuric acid, when present in the waters, must have been un- 

 favourable to aquatic life ; and conversely, wherever organic matter 

 either terrestrial or marine could accumulate, the red colour would be 

 partially removed. Secondly, they show the cause of the almost con- 

 stant association of large quantities of coal and other vegetable re- 

 mains with the carbonate and sulphuret of iron. Thirdly, they may 

 in some cases serve to distinguish marine from freshwater deposits ; 

 since on the above view, sulphurets would be formed in large quan- 

 tity where sea water had access to the beds in which vegetable or 

 animal matter was decaying, while carbonates would prevail where 

 fresh water only was present. In some cases, however, the sulphates 

 afforded by springs, or even by river water, might produce a suffi- 

 ciency of sulphurets to invalidate such inferences. Fourthly, the 

 occurrence of grey beds and patches in red formations may often 

 indicate the former existence of fossils whose forms have perished ; 

 and the quantities of iron pyrites found in some ancient non-fossilife- 

 rous beds may possibly be an indication of the same kind. 



2. Bemarks ypon the Structure of the Calamite. By John S. Dawes, 

 Esq., F.G.S., President of the Lit. & Phil. Soc. of Birmingham. 



[Since this paper was read to the Society, Mr. Dawes has made some 

 further observations u{)on the structure of this fossil, and its full 

 publication is therefore deferred at his request.] 



