TRANSACTIONS OF SECTION C. 327 



some parts of the earth than in others, and the crust movements which so altered 

 the physical geography of the Carboniferous hills, dales, and swamps as to develop 

 a new aspect of nature, terminated the period sooner in some quarters of the globe 

 than in others. In such a locality, however, as Eastern Hindostan, the duration 

 of a Carboniferous type into the secondary ages is apparent. Hence, in spite of 

 a recognised general contemporaneity, it must be credited that Carboniferous, 

 Devonian, Permian, and later deposits were accumulating early r and late during the 

 lapse of one great age in distant parts of the globe. 



The duration of the Carboniferous age in the broadest sense may be attempted, 

 but with no great success, to be estimated by the time which must have elapsed 

 during the world-wide dispersion of identical species ; and its biological relation 

 to the preceding and subsequent formations may be appreciated from the fact that 

 the Carboniferous flora, lasting as it did from the bottom to the top of the forma- 

 tion, was foreshadowed in the Devonian, and that it founded the Mesozoic. Thus 

 the Australian, Himalayan, British and North and South American marine strata of 

 the Carboniferous age contain many identical species of Brachiopoda— the variation 

 from the English types, which were the first described, being very slight. Amongst 

 the corals some forms are equally widely diffused. Now, according to what occurs 

 in nature at the present time, the movement of species from one locality to another 

 by ova, or by wafting of the young — the only method of the lateral or horizontal 

 progress of the Brachiopoda — for instance, is impeded by many physical conditions, 

 and is constantly rendered abortive by predaceous and obstructive living forms, and 

 by what is called the struggle for existence. Migration, or rather the extension of 

 the locality of the species, for the first term implies much more than was or is ever 

 done, is so rarely possible to any great extent under the present complicated natural 

 history and physical condition of the earth, that the mind fails to grasp the time 

 which wovdd lapse between the commencement of the dispersive process and the 

 establishment of identical species, even a few thousands of miles off. To bring the 

 subject a little nearer, however, it is necessary to consider that the Arctic and 

 Antarctic cold areas and the frigid bathymetrical ocean zones did not then exist, 

 and that the movements of the crust, producing extension of coast lines, were 

 exceedingly frequent during the age, and must have facilitated the dispersion of 

 littoral and moderately deep sea species. 



The dispersion of the species of the numerous cryptogamous plants was doubtless 

 rapid in relation to that of the animals, for their spores could be wafted to a great 

 distance by wind, and they do not appear to have had much to struggle against. 

 With the Coniferaa it was different, and the examination of the methods in which 

 fir trees spread in favourable localities at the present time is very suggestive of 

 exceeding slowness of dispersion. Nevertheless, the cones of the Coniferse were 

 carried here and there by water during the Carboniferous age. 



To add to the notion of the long duration of the age it must be remembered 

 that a succession of identical floras occurred nearly on the same areas, involving 

 repetitions of growth and of migration. 



The growing of the vegetation of each swamp and lowland tract, its accumu- 

 lation and covering up with sand, shales, and gravel, occupied much time, and the 

 last process involved the destruction of considerable breadths of plant life. The 

 formation of under-clay or warp, if the similar occurrences of the present day be 

 taken as examples, occupied much time, and then a lapse occurred, whilst the 

 nearest flora supplied a new vegetation to the virgin soil. 



In some instances the recurrence of vegetation was evidently the result of 

 spreading from no great distance ; but in others so great a depth of sediment sepa- 

 rates the consecutive deposits of coal, and the great subsidence which took place is 

 so evident, that the migration must have been from a considerable distance, and 

 must have occupied commensurate time. In endeavouring to appreciate this lapse 

 of time, it must be remembered that, even on the small surface of the United 

 Kingdom, there was land on some parts during the whole of the Carboniferous 

 Age, notwithstanding the diversity of the deposits and the frequent occurrence of 

 marine conditions. 



It would appear that prior to those movements of the earth's crust which ter- 



