When an area like Britain has been studied, the student may proceed to construction of maps of wider regions, and he will find that in doing this, new sets of facts must be taken into consideration, as for instance the occurrence of different faunas on opposite sides of once-existing continental masses, and the problems connected with the present distribution of the faunas and floras. For an instance of the importance of the former distribution of life the reader may consult the twelfth section of the first part of Professor Suess' Das Antlitz der Erde, whilst a good account of the value of recent geographical distribution of organisms in supplying a clue to former distribution of land and sea will be found in Mr A. R. Wallace's Island Life, Chapter xxii.
Should the method suggested above be adopted, the student is likely to acquire a much more coherent idea of the significance of the facts of stratigraphical geology than can be obtained by a mere perusal of the accounts of the strata given in those portions of the various text-books which are devoted to a consideration of the stratigraphical branch of the science.
THE CLASSIFICATION OF THE STRATIFIED ROCKS.
In the succeeding chapters, a general account of the characters of the Geological Deposits of different periods will be given, for the purposes of illustrating the principles to the consideration of which the earlier chapters have been devoted. It is not proposed to enter into a description of numberless details, which would only confuse the student who wished to grasp the main principles, for many facts have been recorded which it is necessary to notice in a comprehensive text-book treating of stratigraphical geology, though their full significance is not yet grasped. The writer, while noting the main characters of the various subdivisions of the different stratigraphical systems, will assume that this work is used in conjunction with some recognised text-book. The stratigraphical portion of Sir A. Geikie's Class Book of Geology gives an admirable general account of the British Strata, while the larger text-book by the same author has a condensed though very full account of the rocks of the stratigraphical column in all parts of the world, and this is supplemented by numerous references to the original works wherein further descriptions may be found. The English edition of Prof. E. Kayser's Text-Book of Comparative Geology, edited by P. Lake, is also well adapted to the wants of the student, and an excellent account of the strata is given in Mr A. J. Jukes-Browne's Handbook of Historical Geology, which may be read with the same author's Building of the British Isles.
The reader who refers to different text-books will be struck with the variations of nomenclature even amongst the larger stratigraphical divisions, for two authors seldom subdivide the geological column into the same number of rock-systems. The following classification will be here adopted:—
| Groups. | Systems. | |
| Cainozoic or Tertiary |  | Recent Pleistocene Pliocene Miocene Oligocene Eocene |
| Mesozoic or Secondary |  | Cretaceous Jurassic Triassic |
| Palæozoic |  | Permian Permo-Carboniferous Carboniferous Devonian Silurian Ordovician Cambrian |
| Precambrian. | ||
A few remarks may be given as to the reason for adopting this classification.