Chap. XV. Conclusion. 427 



already recorded species. Our classifications will come to be, as far 

 as they can be so made, genealogies ; and will then truly give what 

 may be called tbe plan of creation. The rules for classifying will 

 no doubt become simpler when we have a definite object in view. 

 We possess no pedigrees or armorial bearings ; and we have to dis- 

 cover and trace the many diverging lines of descent in our natural 

 genealogies, by characters of any kind which have long been in- 

 herited. Rudimentary organs will speak infallibly with respect to 

 the nature of long-lost structures. Species and groups of species 

 which are called aberrant, and which may fancifully be called living 

 fossils, will aid us in forming a picture of the ancient forms of life. 

 Embryology will often reveal to us the structure, in some degree 

 obscured, of the prototypes of each great class. 



When we can feel assured that all the individuals of the same 

 species, and all the closely allied species of most genera, have within 

 a not very remote period descended from one parent, and have 

 migrated from some one birth-place ; and when we better know 

 the many means of migration, then, by the light which geology 

 now throws, and will continue to throw, on former changes of 

 climate and of the level of the land, we shall surely be enabled to 

 trace in an admirable manner the former migrations of the inhabi- 

 tants of the whole world. Even at present, by comparing the 

 differences between the inhabitants of the sea on the opposite sides 

 of a continent, and the nature of the various inhabitants on that 

 continent in relation to their apparent means of immigration, some 

 light can be thrown on ancient geography. 



The noble science of Geology loses glory from the extreme 

 imperfection of the record. The crust of the earth with its em- 

 bedded remains must not be looked at as a well-filled museum, but 

 as a poor collection made at hazard and at rare intervals. The accu- 

 mulation of each great fossiliferous formation will be recognised as 

 having depended on an unusual concurrence of favourable circum- 

 stances, and the blank intervals between the successive stages ^ as 

 having been of vast duration. But we shall be able to gauge with 

 some security the duration of these intervals by a comparison of 

 the preceding and succeeding organic forms. We must be cautious 

 in attempting to correlate as strictly contemporaneous two forma- 

 tions, which °do not include many identical species, by the general 

 succession of the forms of life. As species are produced and ex- 

 terminated by slowly acting and still existing causes, and not by 

 miraculous acts of creation ; and as the most important of all causes 

 of organic change is one which is almost independent of altered 

 and perhaps suddenly altered physical conditions, namely, the 



