Concerning the other two difficulties, then, the only possible way of meeting that as to the absence of any parent forms lower down in the geological series is by falling back--as in the analogous case of animals--upon the imperfection of the geological record. Although it is certainly remarkable that we should not encounter any forms serving to connect the Dicotyledonous plants of the Chalk with the lower forms of the underlying Wealden, we must again remember that difficulties thus depending on the absence of any corroborative record, are by no means equivalent to what would have arisen in the presence of an adverse record--such, for instance, as would have been exhibited had the floras of the Wealden and the Chalk been inverted. But, as the case actually stands, the mere fact that Dicotyledonous plants, where they first occur, are found to have been already differentiated into their three main divisions, is in itself sufficient evidence, on the general theory of evolution, that there must be a break in the record as hitherto known between the Wealden and the Chalk. Nor is it easy to see how the opponents of this theory can prove their negative by furnishing evidence to the contrary. And although such might justly be deemed an unfair way of putting the matter, were this the only case where the geological record is in evidence, it is not so when we remember that there are numberless other cases where the geological record does testify to connecting links in a most satisfactory manner. For in view of this consideration the burden of proof is thrown upon those who point to particular cases where there is thus a conspicuous absence of transitional forms--the burden, namely, of proving that such cases are not due merely to a break in the record. Besides, the break in the record as regards this particular case may be apparent rather than real. For I suppose there is no greater authority on the pure geology of the subject than Sir Charles Lyell, and this is what he says of the particular case in question. "If the passage seem at present to be somewhat sudden from the flora of the Lower or Neocomian to that of the Upper Cretaceous period, the abruptness of the change will probably disappear when we are better acquainted with the fossil vegetation of the uppermost tracts of the Neocomian and that of the lowest strata of the Gault, or true Cretaceous series[59]." [59] _Elements of Geology_, p. 280.