1845.] 509 



the. lower carboniferous series, it may be useful shortly to describe 

 the various rocks of which it is composed. 



The red sandstones are of various shades, from brick red (which 

 is not common) to reddish brown. They scarcely differ, in their 

 range of colours, from those of the gypsiferous formation, except 

 that' in the latter purplish tints are more frequent. They are often 

 flaggy and micaceous, and obliquely laminated, and there is every 

 gradation, from very coarse sandstone to shale. 



The red shales are generally laminated, but not finely ; occasion- 

 ally, but rarely, they want lamination and then can scarcely be dis- 

 tinguished from the fine sandstones and mudstones which, in the 

 gypsiferous formation, have been named marls. They often have 

 greyish fucoidal marks, and sometimes remains of land plants. 

 The red sandstones and shales are usually soft, and I have no- 

 where seen them attain the hardness so often found in tlie similar 

 rocks of the gypsiferous formation. 



The grey sandstones vary in colour from neutral grey to brown- 

 ish and yellowish tints ; the latter owing to the decomposition of 

 iron pyrites. The sandstones are sometimes coarse, and full of 

 white quartz pebbles, but are more frequently of finer texture. 

 They are accompanied by greyish shales and clays, and the groups 

 of grey sandstone and shale, occurring in the newer coal formation, 

 are much more important than those of the gypsiferous series 

 These groups of grey beds are always accompanied by thin layers 

 of coarse grey limestone, usually wedge-shaped, and consisting of a 

 basis of sand cemented by lime, containing concretions and small 

 fragments of argillaceous limestone. These coarse limestones, and 

 the" sandstones with which they are associated, are always much 

 harder than the red-coloured beds. 



From the constant existence, in the grey sandstones, of carbo- 

 nized plants with sulphuret of iron, it may be inferred that this 

 sulphuret has been produced by the decomposition of the sulphates 

 in sea water, in consequence of the action of decaying vegetable 

 matter, and the combination of their sulphur with iron derived 

 from the surrounding deposits (a process now taking place in many 

 estuaries). By supposing the bleaching of red sands and clays to 

 have been effected in this way, we should, perhaps, account for the 

 connection of fossil remains with grey beds, and for the com- 

 parative absence of red tints from the highly carboniferous rocks 

 of the older coal formation. 



There are at least two beds of limestone in the newer coal form- 

 ation, quite distinct from the impure sandy layers before noticed. 

 The principal stratum, that seen near New Glasgow, is of a grey 

 colour, in some places very dark ; its structure varies m different 

 parts of its thickness, being flaggy above, concretionary below and 

 in the middle, showing a peculiar combination of concretionary 

 and laminated structure, unique among our limestones, and pre- 

 served by this bed as far as it can be traced. The limestones 

 seen at Little Harbour, Pictou Island, Cariboo and Cape John 

 are of a dark grey colour, caused by carbonaceous matter; 



p f 4 



