XXX11. GEOLOGY OF DUMFRIESSHIRE. 



east of the Ewes Water, south-westwards by Langholm to Birrenswark. 

 At the base they consist of conglomeratic sandstones, the included 

 pebbles havingbeen derived from the erosion of the Silurian flagstones 

 and shales ; these are overlaid by friable red sandstones and marls. 



The Old Red Sandstone strata, within the limits of the County, 

 have not proved fossiliferous, but elsewhere in Scotland they have 

 yielded land plants and ganoid fishes. From the lithological characters 

 of the strata and the nature of the organic remains, it was long ago 

 suggested by Fleming, Godwin-Austin, and Ramsay that they had been 

 deposited in lakes or inland seas an opinion which has been generally 

 adopted by geologists. 



Towards the close of the upper Old Red Sandstone period there 

 was a remarkable outburst of volcanic activity on the south slopes of 

 the Silurian table-land, giving rise to an interesting series of igneous 

 rocks that always intervene between the red sandstones and carbonifer- 

 ous strata. They consist mainly of slaggy and amygdaloidal andesites, 

 which were spread over the sea-floor as regular lava flows. They can 

 be traced more or less continuously from the Tarras Water by Langholm 

 to Birrenswark Hill. This picturesque hill is formed of an isolated 

 mass of lava, surrounded by a narrow fringe of upper Old Red Sand- 

 stone. Some of the volcanic orifices from which these igneous materials 

 were discharged are still to be found on the watershed between Tarras 

 Water and Liddlesdale, and another of considerable size on the east 

 bank of the Ewes Water, about a mile north of Langholm. 



The representatives of the carboniferous system by far the most 

 important from an economic point of view occur in three separate 

 areas: (i) in the district extending from Langholm to Ruthwell ; (2) 

 at Closeburn, near Thornhill ; (3) in the neighbourhood of Sanquhar. 

 The first of these is the most extensive, measuring about twenty-two 

 miles in length and varying in breadth from two to seven miles. The 

 following zones, given in descending order, were established in the 

 course of the geological survey of the district : (8) Reddened shales 

 with plants belonging to the true coal measures ; (7) Canobie coals and 

 associated strata ; (6) marine limestone series of the Esk, Penton, 

 Ecclefechan, and Kelhead ; (5) volcanic zone of fine tuff and andesite, 

 including about 50 feet of fine shales ; (4) Woodcock air sandstones ; 

 (3) Tarras Waterfoot cementstone series ; (2) white sandstones under- 

 lain by (i) the andesite lavas of Birrenswark and Ward Law. 



In the course of the geological survey an important discovery of a 

 large number of new organisms was made in the beds of zone 5 and 

 partly in zone 3. The most celebrated locality occurs on the banks 

 of the River Esk, north of Canobie, in a particular band of shale 

 associated with volcanic tuff in zone 5. The fossils are in a splendid 

 state of preservation ; in some instances they have been so protected 

 by their matrix of fine clay as to retain structures which have never 



