32 



and lower coal How far these subdivisions may indi- 

 cate great life-periods, or only portions of one great epoch, has yet to 

 be determined by a more minute and rigorous comparison both of 

 vegetable and animal species, a task which has hitherto been 

 neglected for the lighter labour of popular description and attractive 

 generalization." 



The second group in this arrangement corresponds to Nos. 3 and 

 4 in our division (Art. 17) ; the third corresponds to our fifth, and 

 in it there occur, as with us, intercalated beds of fresh-water origin, 

 consisting chiefly of a mass of cypridae. Our sixth group, the 

 Ballagan series of beds, finds no representative in the eastern fields, 

 though occurring, as already noticed, in a state of less perfect devel- 

 opment in the Merse of Berwick. But to constitute the middle 

 portion into a separate group under the designation of " the moun- 

 tain limestone," appears to us only calculated to mislead the student, 

 and to give a false impression to geologists regarding the true char- 

 acters and great distinctive feature of our lower groups. Thick 

 beds of marine limestone occur at the base, in the middle, and at the 

 top of the series, and contain the same fossils ; while at each end of 

 the series, fresh-water strata are intercalated among the prevailing 

 marine groups.* The entire series of beds thus forms one great 

 natural group of strata, uniform throughout in the character of its 

 often repeated alternations of similar bands of rock, and in its 

 organic contents. Its prevailing character is that of a mechanical 

 deposit, the crystalline limestone bearing an incalculably small ratio 

 to the shales, sandstones, and impure earthy limestones. Yet is 

 this entire series the representative of the great crystalline masses 

 at the base of the coal formation in England and Ireland. The 

 whole group seems to us to be in the place of the mountain lime- 

 stone ; but this rock nowhere exists as a base or geological horizon. 

 This view was first, we believe, put forward at the Edinburgh 

 meeting of the British Association in 1850, but met with con- 

 siderable opposition, and has since been often canvassed. Mr. Miller 

 remarks regarding it as follows :f 



* The marine limestones of the Lennoxtown valley, and white cyprida limestone (/), 

 have been already noticed (Art. 16). Mr. John Young of Lennoxtown also finds a 

 fresh-water limestone among the marine beds at Bishopbriggs ; and very recently 

 (March, 1857), Mr. John M'Diarmid of Glasgow has found within the city, south side 

 of Parliamentary Road, opposite the Town's Hospital, beds of limestone and calcareous 

 sandstone, with numerous marine fossils of the ordinary genera, and fossil plants, at the 

 very top of the marine series, and closely adjoining the fresh-water series of our second 

 division (Art. 17). 



f " The Fossiliferous Deposits of Scotland," being an address to the Royal Physical 

 Society of Edinburgh, delivered November 22d, 1854. Pp. 16, 17. 



