﻿1850.] HARKNESS ON THE SILURIANS OF DUMFRIESSHIRE. 53 



ing-up of the deposits ; but in the case of the soft shales and the an- 

 thracite, there appears to have been considerable strain, by means of 

 which these beds were broken up and contorted. 



The almost constant effect of these faults has been to give the 

 strata a N.N.W. dip. In some localities there are, however, inclina- 

 tions varying from this ; but these occupy a very small area, and are 

 only indications of small local oscillations, and soon give place to the 

 prevailing dip ; and so general is the direction of the faults along the 

 course of the strike, that in the Stewartry of Kirkcudbright, where 

 igneous rocks abound from whence veins both of granite and por- 

 phyry emanate, the course of these veins is almost universally that 

 of the range of the strata. 



Having seen the intimate connection which exists between these fos- 

 siliferous bands, the question presents itself, as to what portion of the 

 Silurians are they referable. The organisms which are found in the 

 greatest quantities are Graptolites ; and, since these are but low in 

 the scale of Radiata, it is probable that they may have an extensive 

 geological range, as we find Graptolites Ludensis, Murch., ranging 

 from the Ludlow rocks to the Llandeilo flags. Some of these fossils 

 appear to be more restricted in their position, and particularly that 

 portion of the group which are foliaceous and have serratures on both 

 sides. To these latter fully one half of the species which occur in 

 Dumfriesshire appertain, and consequently they mark to a certain 

 extent the position of the deposits in which they abound. Amongst 

 the Irish Silurians in which Graptolites are met with, Colonel Port- 

 lock considers those beds which contain such as have serratures on 

 one side only, as lying beneath the deposits which afford such as have 

 a foliaceous character ; and Prof. Nicol, applying the same principle 

 to the graptolite beds of Peeblesshire, considers that the deposits at 

 Grieston quarry in that county are referable to the Llandeilo flags, 

 and that the beds described by Mr. Moore, and occurring in Wigton- 

 shire, in which foliaceous Graptolites are found along with three 

 species which have serratures only on one side, similar to some of 

 those at Grieston, occupy a higher position than the Peeblesshire 

 fossils. With regard to the Dumfriesshire Graptolites, they seem, 

 with the exception of one or two species, to be distinct from any of 

 those which have been procured either from Grieston or Wigton- 

 shire ; and, on the whole, the foliaceous group is so well developed, 

 as to place them in a higher position than even those of the latter 

 locality. I am, therefore, induced to consider the deposits which 

 they occupy as the equivalents of the Caradoc sandstone. 



The general mineral nature of the deposits which represent the 

 Silurian rocks in this county consists of greywacke sandstone and 

 indurated shales, as before stated. These are, however, with some 

 slight modifications, the common characters of the whole of the Si- 

 lurian formation in the south of Scotland, and have originated in the 

 same causes which have produced the sandstones and shales of other 

 geological formations. 



Of the peculiar feature of this deposit in Dumfriesshire, viz., the 

 anthracite bed and its overlying dark shales, the origin is not alto- 



