103 ROCK-METAMORPHISM. 



satisfied, however, that the group contains formations referable 

 in the main to the different stages of a cycle of vertical move- 

 ments, I cannot but regard it as of systemal rank, though 

 I admit that it cannot be equalled in comprehensiveness with 

 certain other rock-systems. 



The following table exhibits a series of formations representing 

 the different stages, as successively developed in the course of a 

 cycle of vertical movements which took place during the Permian 

 period : 



Lancashire Triassic Bunter sandstones. 

 5th Staff e. St.-Bees (Whitehaven) red sandstones. 



4:th Stage. Manchester marls and thin-bedded limestones. 



Yorkshire and Barrowmouth (Cumberland) Schizodtis-limstones 

 and gypseous marls. 



Sunderland coralloidal limestones. Hartlepool and Marsden lime- 

 stones. Ardtrea (co. Tyrone) magnesian limestone. 



3rd Stage. Humbleton (.Durham) fossiliferous limestones. 



2nd Stage. Midderidge (Durham) compact limestones. 

 Durham marl-slate. 



\st Stage. Pontefract sandstones. Solway red-sandstones. 

 Westoe (Durham) >%^rm-sandstones. 



Coal-measures of the Carboniferous system. 



chronous formations in separated areas of one and the same region, and the 

 vast difference in thickness of the rocks severally constituting the different 

 systems. 



Rock-systems are often deficient in formations representing the 1st and 5th 

 stages : such are usually tripartite, as the Triassic ; though in some instances 

 of the kind the missing formations have doubtless been removed by denuda- 

 tion, which, as will be readily understood, must be energetic during these 

 two subaerial stages. The Carboniferous system may be taken as an example 

 in which all the stages, especially the 1st and 5th, are well represented. 

 The Triassic system, which on the continent comprises three formations cor- 

 responding with the 2nd, 3rd, and 4th stages, is in the British Isles devoid 

 of any representative of the middle one (3rd) of these stages. On the other 

 hand, this stage is well developed in the Cretaceous system of the south of 

 England and other countries; but the 5th stage is poorly represented 

 in most regions, except, seemingly, in the Rocky Mountains and the more 

 western ranges, where occur intercalated formations containing Ammonites 

 Baculites, &c., and Tertiary plants, which indicate the missing time-link 

 between the Cretaceous and Eocene periods. (See Prof, J. Stevenson 

 American Philosophical Society, June 18, 1875.) 



