CHAP. XV.] CONCLUSION. 401 



of use and disuse, on the direct action of external conditions, and 

 so forth. The study of domestic productions will rise immensely 

 in value. A new variety raised by man will be a more important 

 and interesting subject for study than one more species added to 

 the infinitude of 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 the 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 discover and trace the many diverging 

 lines of descent in our natural genealogies, by characters of any 

 kind which have long been inherited. Rudimentary organs will 

 speak infallibly with respect to the nature of long-lost structures. 

 Species and groups of species which are called abberrant, 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 proto- 

 types 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 

 inhabitants 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 im- 

 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 

 accumulation of each great fossiliferous formation will be recog- 

 nised a-s having depended on an unusual concurrence of favourable 

 circumstances, 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 con- 

 temporaneous two formations, which do not include many identical 

 species, by the general succession of the forms of life. As species 

 are produced and exterminated by slowly acting and still existing ^ 

 causes, and not by miraculous acts of creation ; and as the mast 



