TEANSACTIONS OF SECTION C. 617 



a yet further continental extension towards the south-east. A great epoch of 

 mountain-making in the Scotch Highlands, which had perhaps heen going on at 

 intervals from the beginning to the close of the Silurian period, had now come to 

 an end ; the southern uplands had risen up, like a Jura to the Alps. But probably 

 their elevation did not terminate the earth-movements, for the post-Silurian 

 cleavage of the Lake district, and the absence of Old lied Sandstone both here and in 

 Central England, indicate that the Palteozoic land mass continued to extend on 

 its south-eastern flank. The Devonian period introduces us in the greater part of 

 Great Britain to an epoch of limited and exceptional deposits, and of widely preva- 

 lent terrestrial conditions. It seems almost certain that the Old Red Sandstones 

 of Scotland and Wales are of fresh-water origin — the deltas of rivers, formed 

 either in lakes or possibly in part as sub-aerial deposits. Streams of considerable 

 volume and of some strength are indicated by the materials. In one case, the Old 

 Red Sandstone of North-east Scotland, we may perhaps discern in the Great Glen 

 some indication of the old river-course. It is easy to ascertain the source of the 

 materials of the Scottish Old Red Sandstones. They are as obviously the detritus 

 of the Highland mountains — then probably a far grander and loftier chain — as 

 the nagelflue and the molasse of Switzerland are of the Alps. 



At this time marine conditions prevailed in the south of England. The sea 

 appears to have deepened towards the south, but I suspect that a region of 

 crystalline rocks still existed at no great distance in that direction and in the west. 

 Probably the Brito-Scandinavian Peninsula curved round to the east so as to 

 include some part of Brittany.* Another great epoch of subsidence now com- 

 menced, commemorated by the formation of the Carboniferous limestone. At this 

 I need hardly glance, as it has been so fully discussed by Professor Hull and other 

 writers. The land sank both in the north and in the south of England. There was 

 deep sea over Derbyshire and Southern Wales, but the ground beneath our feet 

 probably remained above water, forming either a continental promontory or a 

 large island. 



There were other well-known interruptions to the sea, which also overflowed a 

 considerable part of Ireland and districts far to the east of England. The Scotch 

 Highlands, however, probably remained above water, for, as is well known, the 

 Carboniferous limestone of Central Scotland overlies a fresh-water formation, and is 

 itself not wholly marine, since it contains coal, and like conditions prevailed in 

 Northumberland . 



Gradually, however, the sea shallowed, and terrestrial conditions returned. In 

 the later part of the Carboniferous series we have clear indications of two, or 

 perhaps three, important currents, almost certainly those of rivers, bringing 

 materials, in the southern district from the west ; in the northern, from the north- 

 west and probably the north-east. These materials may have been in part derived 

 from older Palaeozoic rocks, but the facts when carefully considered seem to indicate 

 that there was also an extensive denudation of crystalline and not improbably 

 Archaean rocks, unless we suppose that great areas of eruptive Palaeozoic granite 

 have now disappeared beneath the waters. At any rate, we may perhaps regard 

 the open water between Ireland and Scotland on the one hand, and to the east 

 of the latter country on the other, as significant of a denudation earlier than that of 

 the sea which has in later times divided the British Isles. Another epoch of earth- 

 movements closed — as was to be expected — the Carboniferous subsidence and 

 deposition. We trace one line of flexures and of intense compression along a 

 broad zone, including the south of England, from Germany to Ireland ; another less 

 intense over the northern part of our country ; the axes of the former flexure 

 striking a little N. of W., of the latter about W.S.W. The one appears to me to 

 indicate a thrust from a great mass of hard, more or less crystalline rock in the S., 

 which probably led to the formation of a mountain chain extending fi-om North- 

 central Europe over the Channel to the southern margin of England. The latter 

 may be explained by the presence of the above-named north-western continent. 



' Compare, as an illustration, the curving round of the Alpine chain on the 

 western side of Italy. 



