168 rPvOCKEDIXGS OF THE GEOLOGICAL SOCIETY, 



the land began once more to sink ; and brackish-water formations 

 appear, followed later on by purely marine deposits. The Car- 

 boniferous shales and Mountain Limestone cover the former land 

 with its imbedded plants. The great extension of the Mountain 

 Limestone over many parts of Europe and America, and the small 

 number of land formations which it covers, show us that this 

 sinking of the land must have been a general phenomenon. The 

 northern hemisphere must therefore most probably have had quite 

 a different aspect at that time than during the Ursa stage. Then the 

 same phenomenon recommenced as in the beginning of the Carboni- 

 ferous period. In consequence of an extended rise to the west we 

 obtain the continental formations of the Millstone-grit, which after- 

 wards reached their greatest extent and development in the Coal- 

 measures. During this long lapse of time the flora remained, on 

 the whole, the same. Many of the leading species outlived all the mu- 

 tations, and shoAV that the whole of the land was never under water, 

 even at the time of the formation of the Mountain Limestone ; there 

 always remained enough dry land to support these species of plants, 

 which afterwards extended their range when the land, as in the 

 Millstone-grit, began again to have a greater extension. There 

 can be no doubt that a long period must have elapsed between the 

 beginning of the Ursa stage and the Millstone -grit, and that during 

 these many thousand years the conditions of life of the organic 

 beings must have undergone reiterated changes. It is therefore a 

 very remarkable fact that, in spite of this, so many species lasted 

 through this time and did not undergo any perceptible alteration. 

 The many forms of Ccdamites radiatus which appear in Bear Island 

 are also found in the lowest member of the Lower Carboniferous 

 and in the roofing-slates of Moravia ; then the species disappears, nor 

 does any similar form of this type (which Schimper has raised into a 

 separate genus, Bornia) extend into the Coal-measures ; the same 

 thing takes place in the species of Knorria and Gardioj)teris. These 

 facts tell very decidedly against the continuous and imperceptible 

 transmutation of plant-species. They are the more important, 

 since the plants on Bear Island must clearly have lived under quite 

 different conditions of light than those in the Yosges or in Ireland; 

 for they must have endured a long winter-night. It is indeed re- 

 markable that evergreen trees, such as the Lepidodendra must 

 probably have been, and plants with such large leaves as Car- 

 diopter is frondosa could have withstood such a long winter-night, 

 even if we take into consideration that the Bear-Island flora con- 

 sisted almost entirely of vascular Cryptogams, which can better 

 dispense with light than the Phanerogams. Moreover the climate 

 of Bear Island must have been as favourable to the growth of 

 l^lants as that of Ireland or the Vosges, although that island lies 26^° 

 further north ; for the corresponding species are as large and quite 

 as luxuriantly developed, and have even produced more consider- 

 able coal-strata than those of lower latitudes in the same period. 

 Warmth, therefore, must at that time have been more equally dis- 

 tributed over the earth, whilst already in the Miocene period a 



