236 ON THE NATURAL HISTORY OF THE SOUTH OF SCOTLAND. 



and Roses in these valleys, in which, as in other respects, they differ essentially 

 from the glens of the Grampians. 



The more common direction of the strata in Ettrick is S.W. and N.E., and 

 th eir inclination to the N.W., but both are various. In the vallies of Ettrick 

 and Yarrow there are no precipices, nor in fact many exposed portions of rock, 

 excepting those in the streams. It is also singular that no rolled blocks are to be 

 seen of the diameter of three feet. 



The Ettrick receives the Yarrow below Bowhill, about two miles above 

 Selkirk, and their united streams enter the Tweed a mile above Abbotsford, 

 where we leave the river to pursue its course towards the ocean. 



Perhaps few districts in Scotland of equal extent present fewer interesting 

 geological phenomena than that which contains the sources of the Tweed. Ex- 

 cepting the limestone at Crook, I have not heard that any of the strata have been 

 found to contain organic remains ; nor are such mentioned in any of the Statis- 

 tical Reports, which, however, are in general extremely deficient in every thing 

 that relates to Natural History. « 



We have seen that the whole district, so far as it has been examined, is com- 

 posed of grey-wacke, grey-wacke slate, clay-slate, and slate-clay, passing into 

 each other, or alternating, distinctly stratified, often laminar, and frequently 

 presenting plates of extreme tenuity. The general direction of the strata is 

 from S.W. to N.E. They are usually much inclined, sometimes vertical, and 

 not unfrequently horizontal, but present every degree of inclination. The general 

 dip is to N.W. 



The composition of the grey-wacke exhibits considerable variety. Sometimes, 

 as in the upper part of Eddlestone Water, it is a very closely aggregated frag- 

 mentary rock, composed of white crystalline quartz, brown and red jasper, black 

 Lydian-stone, grey or bluish flinty-slate, and pieces of dark-coloured shale, 

 impacted in a fine-grained greyish basis. The fissures are filled with indurated 

 argillaceous matter, and dark green unctuous earthy chlorite. Particles of mica 

 and felspar are sometimes seen in the mass, of which the aggregation is often less 

 perfect when it approaches in character to a conglomerate. 



More frequently, when the rock is large-grained, it is of a bluish-grey colour, 

 mottled with white, more crystalline, but still evidently fragmentary. The basis 

 is small-grained, grey, with large fragments of compact or slaty rocks of the 

 same, colour, or sometimes of dark shale, interspersed. The impacted substances 

 are white and grey quartz, with very few fragments of a different colour, some- 

 times small crystals of calcareous spar, and a few particles of mica. Veins of 

 quartz and calcareous spar often intersect this variety. 



From this it passes into a rock presenting at first sight, on its recently-exposed 

 surfaces, the appearance of a green-stone, but still composed of the same ingre- 



