and Belations of the Frontier Chain of Scotland. 251 



of determining (on the principles laid down by Professor 

 Rogers of America) the line from which the undulations had 

 originated. He also (being himself crippled in 1849) em- 

 ployed Mr John Ruthven in making out a detailed section on 

 the line of the railroad from Carlisle to Edinburgh (carefully 

 noting the steep sides of the successive undulations), and in 

 collecting fossils. The evidence of the coast sections of St 

 Abb's Head, the author has not examined personally since 

 1830, and dares not, therefore, pronounce any decided opinion 

 on their bearing on the question of the mineral axis of the 

 chain. On the whole of the evidence he, however, proposes 

 (not without much doubt and hesitation) to separate the chain 

 into the following groups, beginning with the lowest. 



II. — Successive Groups in ascending order. 



(1.) A great group, always in a highly inclined position 

 (and often so nearly perpendicular that it is very difficult 

 to know whether we are reading off the details in an ascend- 

 ing or descending order), in which a pyritous alum-schist 

 abounds, sometimes so much that the coarse, hard, arenaceous 

 beds become subordinate to it. In other places the schist 

 becomes subordinate, indurated, and passes into a coarse 

 slate or flagstone. The group ranges from the neighbour- 

 hood of Lockerby till it is succedeed by a superior group 

 (north of Moffat) on the line of the railroad. It stretches 

 into the high hills connected with Hart Fell, and into the 

 ridges forming the water-shed of the Moffat water and the 

 Yarrow. But its limits to the north-east and south-west 

 are not ascertained. Through the alum-slates of this group 

 (the Moffat Group) are innumerable graptolites, well pre- 

 served, and of many species. Its whole thickness is great, 

 but the estimate is made difficult by the undulation. 



(2.) A great arenaceous group with bands of earthy flag- 

 stone and coarse slate, a part of which is well exposed in 

 numerous undulations, in the cuttings of the railroad. The 

 author thinks that this second great group passes into 

 Peeblesshire and the upper part of the valley of the Tweed, 

 and that it thence extends to St Abb's Head. He wishes 

 also (but not without hesitation and a very inadequate evi- 

 dence) to spread this group through a considerable part of 



