The state of our knowledge, and the slowness of the changes of level, do not permit us to test the truth of these remarks, by observing whether there are more transitional or "fine" (as naturalists would term them) species, on a rising and enlarging tract of land, than on an area of subsidence. Nor do I know whether there are more "fine" species on isolated volcanic islands in process of formation, than on a continent; but I may remark, that at the Galapagos Archipelago the number of forms, which according to some naturalists are true species, and according to others are mere races, is considerable: this particularly applies to the different species or races of the same genera inhabiting the different islands of this archipelago. Furthermore it may be added (as bearing on the great facts discussed in this chapter) that when naturalists confine their attention to any one country, they have comparatively little difficulty in determining what forms to call species and what to call varieties; that is, those which can or cannot be traced or shown to be probably descendants of some other form: but the difficulty increases, as species are brought from many stations, countries and islands. It was this increasing (but I believe in few cases insuperable) difficulty which seems chiefly to have urged Lamarck to the conclusion that species are mutable. CHAPTER VII ON THE NATURE OF THE AFFINITIES AND CLASSIFICATION OF ORGANIC BEINGS{425} {425} Ch. XIII of the _Origin_, Ed. i., Ch. XIV Ed. vi. begins with a similar statement. In the present Essay the author adds a note:--"The obviousness of the fact (_i.e._ the natural grouping of organisms) alone prevents it being remarkable. It is scarcely explicable by creationist: groups of aquatic, of vegetable feeders and carnivorous, &c., might resemble each other; but why as it is. So with plants,--analogical resemblance thus accounted for. Must not here enter into details." This argument is incorporated with the text in the _Origin_, Ed. i. _Gradual appearance and disappearance of groups._