﻿1850.] HARKNESS ON THE SILURIANS OF DUMFRIESSHIRE. 57 



From these south inclinations of the strata along the southern 

 margin of the Silurians, and from the N.N.W. dips which succeed 

 them on the north, it is evident that an anticlinal axis traverses the 

 range near its southern extremity ; and this axis seems to have 

 resulted from the granitic eruption of CrifFel, which has split the 

 strata in an east and west direction, and elevated the deposits along 

 this line of fracture. From the same cause, in all probability, origi- 

 nated the numerous faults which run along the equivalents of the 

 Caradoc sandstone in Dumfriesshire. In that portion of the Silurian 

 chain which occurs in the southern parts of Peeblesshire we have the 

 south dip again prevailing ; so that it appears that between the 

 N.N.W. inclinations of Dumfriesshire and the south dips of the 

 former county, there runs a synclinal axis ; and according to Prof. 

 Nicol, a northerly dip prevails along the northern boundary in 

 Peeblesshire, showing the occurrence of a second anticlinal axis near 

 the northern boundary of the Silurians in that county. 



Many local variations from the usual inclinations are met with in 

 different parts of the chain ; one for instance is seen in Dumfries- 

 shire, in the cutting of the Glasgow and South-western railway, about 

 five miles east from Dumfries ; and as this is the most southerly 

 exposure of the Silurians in this county, the section is one of con- 

 siderable interest. The railway here is cut through the southern 

 base of an outlying hill, called the Howthat, which forms a spur 

 from the general direction of the chain. Commencing at the west 

 end of the cutting, we have beds of indurated shale, considerably 

 metamorphosed, each bed being about three inches in thickness, 

 dipping S.S.E. at an angle of 70°. This dip continues for some 

 distance, and as we proceed eastwards the shale has thin beds of fine- 

 grained greywacke sandstone intercalated in it, the faces of the sand- 

 stone being in many cases ripple-marked. These beds afterwards 

 assume a perpendicular position, and soon the inclination is towards 

 the N.N.W. at a high angle. Further east the beds again become 

 perpendicular, and near the end of the section the strata show fine 

 instances of flexures, which are succeeded by a S.S.E. dip. 



Taking a general view of the Silurians of the south of Scotland, 

 our present information would lead me to conclude that they afford 

 the representatives of this system arranged as follows, viz. : On the 

 south margin the Wenlock shales are indicated by the Balmae beds, 

 which have a south dip. Then passing over a district occupied by the 

 granitic axis, having on each side metamorphic rocks, we come upon 

 the equivalents of the Caradoc sandstone, having a continuous N.N.W. 

 dip, and appearing to extend through the central portion of the chain. 

 To the north the Llandeilo flags are represented by the graptolite 

 and trilobite beds of Peeblesshire, described by Professor Nicol. 



With regard to the ages of the axes of this formation there exists 

 considerable difficulty. The granitic and porphyritic eruptions of 

 Galloway must have taken place after the deposition of the Wenlock 

 shales, because this deposit has been thrown up by these igneous 

 rocks ; and, as we have no trace of this portion of the Silurians on 



