c. lap worth on the moffat series. 241 



Introduction. 



§ I. General characters of the Lower Silurian Rocks of the south of 



Scotland. 



No single geographical region in Britain is more clearly defined 

 physically than the broad tableland known as the Southern High- 

 lands or Uplands of Scotland. Cut off abruptly from the north of 

 England by the shallow inlet of the Solway and the mountain-wall 

 of the Cheviots, and from the main mass of Scotland by the great 

 central valley of Lanark and Midlothian, it stretches like a vast 

 zone across the entire breadth of the island from sea to sea. Occa- 

 sionally some of its higher points are sufficiently grouped together 

 to be classed popularly under a common title, such as the Moorfoots, 

 Lowthers, and Lammermuirs ; but the region, as a whole, may best 

 be described as a rolling sea of broad rounded hills and deep narrow 

 valleys. The only level spots occur along the banks of its few really 

 important rivers, where their lower valleys expand into the long 

 fertile reaches of which the Merse, Nithsdale, and Annandale are 

 the most familiar examples. The more elevated areas, which rarely 

 exceed 2000 feet in height, show here and there strips of peat moss 

 or heathery moor-land. Nowhere, however, do we meet with the 

 crag, cliff, and rocky ground of the Northern Highlands, but hill 

 and dale are clothed alike in a universal mantle of soft green turf. 

 The district is consequently preeminently pastoral, agriculture being 

 almost entirely restricted to the low-lying, open dales. 



The rocky floor of the whole of the Southern Uplands is formed 

 of strata of Silurian age. Buried once, either wholly or in part, be- 

 neath portions of the Old Red Sandstone, Carboniferous, and Per- 

 mian, these ancient deposits have again been bared to the action of 

 the elements, which have carved them into that chaos of mountain 

 and valley they now present. The largest surviving fragments of 

 these later formations are the Red and Yellow Sandstones of the 

 valley of the Tweed, and the Carboniferous and Permian rocks of 

 the basin of the Solway. The remainder are mere local patches, 

 scattered along the lines of the chief river-valleys. 



Making exception of the narrow belts of altered strata that sur- 

 round the granitic bosses of Kircudbright and Dumfries, these South- 

 Scottish Silurians are as little metamorphosed as the equivalent 

 deposits of Wales and the West of England. It might therefore be 

 expected that the task of unravelling the physical and zoological 

 succession among them would be correspondingly simple and easy. 

 Unfortunately, however, such is far from being the case. Everjr- 

 where possessed of an accountable similarity in their lithological 

 characters, totally destitute of fossils except in a few isolated locali- 

 ties, and, above all, thrown into the most violent folds and contor- 

 tions, these ancient strata have been shunned by the majority of 

 Silurian geologists, and their sequence has been very differently in- 

 terpreted by the few who have hitherto examined them. 



Of the extraordinary corrugations into which the whole of the 

 South-Scottish Silurians are thrown it is needless to attempt any 



