106 MEMORIAL SKETCH. 



the range of variation of each reputed species, as one of the 

 most essential features of its character ; whilst our ablest 

 Palaeontologists have laboured with success in tracing the 

 identity of numerous species whose remains occur in forma 

 tions stratigraphically distinct. It was, indeed, a favourite 

 doctrine of the late Professor Edward Forbes, that there was a 

 constant relation between the range of any species in space and 

 its range in time ; i.e. that in proportion as the constitution of 

 any species adapted it to diversities in climate, food, etc., so as 

 to permit its extension over a wide geographical area, in that 

 proportion would it have been able to accommodate itself to 

 changes in the same condition, so as to hold its ground through 

 successive geological periods. Further, it had come to be per 

 ceived that where the stratigraphical continuity is the closest, 

 there is the greatest resemblance between the successive faunae, 

 as in the case of the different members of the Cretaceous 

 series ; and further, that where there is an interruption to such 

 continuity in one locality, the gap is often bridged over else 

 where. And even as regards those great separations which 

 were reputed to mark the terminations of the Palaeozoic and of 

 the Mesozoic series respectively, it was generally believed by 

 geologists of the newer school that the interruption was more 

 apparent than real ; depending merely on the want of inter 

 mediate beds in that small portion of the globe which has been 

 hitherto explored. A geologist who has formed his notions of 

 stratigraphical succession from a country where Tertiary strata 

 immediately overlie Silurian, would find that tremendous hiatus 

 in great degree filled up by the intermediate series presented in 

 England alone ; and, in like manner, if the British geologist 

 could carry his researches into areas which were submerged 

 when Palaeozoic and Cretaceous Europe were above the sea, he 

 could doubtless find abundant evidence of gradational passage 

 to the Mesozoic and Eocene. Such gradations, it is now well 

 known, are not wanting within the limits of Europe, and are 

 very obvious elsewhere. 



Even in the pre-Darwinian epoch, then, many of our most 

 thoughtful naturalists were disposed to admit (i) that no definite 

 limits can be assigned to the variation of any species without 



