While travelling over the country it may be noticed that the land is not uniformly fertile. In some places there is greater luxuriance and greater variety of plant life than in others. The question which such observations call forth is what is the cause of these differences? An attempt has been made to give some sort of answer to this question in the following manner:—A limited area has been selected which is traversed by a number of geological formations, and the plants growing on that area have been catalogued. The area selected in the present instance is the county of Surrey, that being the county which is best known to me. Surrey is too small a county to have any difference of climate. The differences of altitude would probably bring about some variety in the flora, but the differences of latitude could scarcely have any appreciable effect. The county is, however, large enough to include a dozen different rock formations within its boundary, and it seems fair to presume that these may have a considerable influence in determining the distribution and variation of its flora.