﻿1851.] MURCHISON SILURIAN ROCKS OF SCOTLAND. 165 



we have not yet sufficient grounds for inferring that the highest lands 

 of this tract, from whence the Tweed, the Clyde, and the Annan 

 descend, and which form the real geographical axis or watershed, are 

 also the oldest strata. All inferences drawn from physical appearances, 

 except the indisputable fact of great undulations and breaks, must 

 indeed be deceptive, when we find that none of the South Scottish 

 anticlinals are persistent for great distances. In one tract, as in the 

 West of Ayrshire, the strata of a given structure dip more to the 

 S.S.E. than to the N.N.W., and near Moffat nearly all the beds dip 

 to the N.N.W. As yet, therefore, there is no possibility of absolutely 

 determining by order of infraposition which is the lowest or oldest 

 mass of stratified rock in the whole of the South of Scotland. 



If we take the mineral character of the rocks, there are copious 

 conglomerates peculiar to the Ayrshire tract, aluminous and an- 

 thracite shales in the central or Moffat country, and fine greywacke 

 and clay-slate in the eastern region. Then, if we turn to the ig- 

 neous rocks, we find serpentines and diallagic traps on the west at 

 Girvan, granites cutting through as a transverse band from Criffel to 

 Loch Doon, trap-dykes clearly posterior in Dumfries, bedded por- 

 phyry in Peebleshire, and massive amorphous porphyry and syenite 

 in Berwickshire. With such diversity of original conditions and 

 many subsequent modifications, very complex results must be ex- 

 pected. Amid these difficulties, we do know, however, that strata of 

 vast thickness, including schists with limestone, and sandstone and 

 grit with conglomerates, are charged with Lower Silurian fossils, and, 

 as a whole, and after many undulations, are overlapped by other 

 schists and slaty rocks in Kircudbright, in which Upper Silurian 

 types of life prevail. When we come to examine this point more 

 closely, and to be guided as we must be in so tortuous and convulsed 

 a region by our only very sure guides, the organic remains, we find 

 that, just as the convolutions prevent us from recognising either the 

 distinct top or bottom of the whole Silurian series, so also the animal 

 remains pertain, as they ought, chiefly to what must be called the 

 central and lower portion of the Silurian system, if classification be 

 regarded on the same broad scale in which it has been applied to the 

 British Isles, Scandinavia, Russia, Bohemia, and America. 



When I penned the first chapters on the Geology of Russia which 

 treated of Silurian rocks in general, and also in previous communications 

 to the Geological Society, I endeavoured to show (1844), that whilst the 

 absolute zoological base of the Silurian system was wanting in Russia, 

 and had not then been defined in the British Isles, it had, when fol- 

 lowed northwards into Scandinavia, a true and indisputable existence. 

 There, grits and arkose, made up of the oldest crystalline rocks of 

 that region, are surmounted by schists and limestones, in which the 

 presence of the genera Olenus, Agnostus, and Paradoxides, with other 

 palaeozoic fossils, marked, as I contended, the earliest zone of recog- 

 nizable life. The admirable researches of our Government geologists 

 have since developed precisely the same facts in North Wales, where 

 the Harlech grits, overlying the unfossiliferous Cambrian slates, are 

 surmounted by a zone containing the Olenus and Paradoxides with 

 Lingulce. The first- mentioned genus had, indeed, been previously 



