1856.] 



HARKNESS — PERMIAN ROCKS OF SCOTLAND. 



261 



In the course of the Glasgow and South-western Railway, we 

 have the sandstones exposed twice in the cutting between the Thorn- 

 hill and Carron Bridge Stations, and one of these exposures presents 

 a troughing of the beds. North of Carron Bridge Station, in the 

 cutting at the south entrance of the Drumlanrig tunnel, we have the 

 sandstones and accompanying strata well exposed. The beds here 

 dip south, at an angle of about 1 2° ; and besides sandstones we have 

 breccias of an interesting character. The south end of the tunnel 

 consists of amygdaloidal trap ; and on the south side of this we have 

 the breccias composed of fragments of the igneous rocks in great 

 abundance ; and these, with the associated sandstones, dip from the 

 amygdaloids. See Section, fig. 3. At the north end of the tunnel, 



Fig. 3. — Section at the South Entrance of Drumlanrig Tunnel, 

 Carron Bridge Station, Dumfriesshire. 



b. Sandstones and Breccias. 

 a. Trap-rock. 



we have variegated Carboniferous grits, dipping S.S.E., at an angle 

 of 25° ; and through these grits the igneous rock has burst. 



The occurrence of igneous rocks here, and the relations which 

 these bear to the Carboniferous beds, as well as their connexion 

 with the newer sandstone strata, are subjects of interest, as we are 

 enabled, to some extent, to derive information concerning the age of 

 the latter ; and this is more important as we shall find in another 

 district the sandstones and breccias occurring under like circumstances. 

 The relations which exist between these several rocks show that the 

 outbursts of trap were anterior to the deposition of the sandstones and 

 breccias ; and this does not appear to be a mere local occurrence, but 

 tends to support the inference that the Coal-fields of the centre of 

 Scotland had not only been deposited, but had been subjected to all 

 those violent disturbances, and outbursts of igneous matter, which 

 are so prevalent among them, before the deposition of the sandstones 

 and breccias. 



As in the other areas of sandstone which are found in Drumfries- 

 shire, we have no proofs that the causes which disturbed them have 

 affected the Silurians surrounding this area ; but the intermediate 

 Carboniferous strata partake to a great extent of the influences of 

 the forces which have disturbed the newer formation. From the 

 appearance of the breccias in the lower portion of these deposits, I 

 am disposed to consider them as the equivalents of the lower and 

 middle portion of the Corncockle series. 



