Senry Sicks — O^i the Northern Talmozoic Rocks, 217 



depression recognized to have been marked in Cambrian times were 

 not wholly obliterated in the Upper Silurian. The lines of migra- 

 tion of the faunas indicated in my former paper remained also 

 apparently still to be the prevailing ones. The Cambrian and 

 Silurian epochs seem to have been parts of the greater Palaeozoic time, 

 perfectly natural in their order of succession, and showing no signs 

 of want in continuity when not interfered with by local changes. 

 In Britain, as we have seen, the succession was checked in limited 

 areas ; but even here, generally, it cannot be said that any intervals 

 of time are unrepresented by stratified formations, as supposed by 

 some geologists. I would rather say that not only are all the 

 lesser epochs represented in parts of this area (South Wales, etc.), 

 the first or nearly so of all the European areas to become submerged ; 

 but that in addition, so far as sediments are concerned, some of the 

 epochs here have an exaggerated importance from the presence of an 

 excess of material derived from volcanos, and from the islands 

 formed by the uplifted portions of the sea-bottom. 



Devonian and Carboniferous. — The physical conditions of these 

 later epochs of the Paleeozoic have been so frequently and so fully 

 treated of by such eminent authorities as De la Beche, Sedgwick, 

 Murchison, Eamsay, Prestwich, Etheridge, Geikie, etc., in Europe, 

 and by Logan, Dawson, Dana, etc., in North America, that it will 

 be only necessary for me to refer very briefly to them. The condi- 

 tion in the early part of the Devonian was like that at the close of 

 the Upper Silurian, and the depression continued to go on regularly 

 and uninterruptedly at this time in most parts of the Northern 

 Hemisphere. It appears to have gone on persistently also to the 

 close of the epoch in some areas, but in others about the middle, and 

 from that to its close great changes took place, and the sea-bottom 

 was there again raised above the sea-level. Volcanic outbursts also 

 took place at this period, and a considerable amount of volcanic 

 material was spread out, forming, in some places, islands in the sea, 

 as between the Grampians and the Tay in Scotland, etc. The dis- 

 turbances during this epoch, like those at the close of the Lower 

 Silurian, occurred chiefly in the western areas in Europe, and along 

 the eastern borders of North America. The difi'erences which are 

 now observable in the sediments belonging to this period in various 

 parts were produced by, and hence dependent upon, the local changes 

 that had taken place. In the undisturbed submerged regions lime- 

 stones alone were formed, as in the previous epoch. Near the 

 uplifted portions, sandstones and the usual materials to be derived 

 from denudation, were deposited. 



These changes gave an entirely new aspect to the Northern 

 Hemisphere, and before the close of the epoch large areas of dry 

 land and numerous lakes and inland seas extended in many direc- 

 tions. During the Carboniferous epoch, most of these areas were 

 again depressed, and marine sediments very generally deposited. 

 "Where the-sea bottom remained undisturbed, as in South Wales, 

 Devonshire, etc., the sediments belonging to these two epochs are 

 perfectly conformable to one another; but in the disturbed areas 



