GEOLOGY. 247 



living beings, began prior to those geological cnanges which gave 

 rise to the unconformity, and prove the gap ; implies, further, that 

 all this went on in some area not necessarily adjacent, but so 

 situated as to ensure the continuity by descent of the organic 

 forms. To admit this, seems to concede the chief point at issue ; 

 and the concession seems involved in the uncontradicted belief 

 held by geologists, that further research will disclose more and 

 more strata requiring to be " intercalated " between those of exist- 

 ing classifications. Geologically this jshrase is unfortunate, though 

 zoologically correct. The oi-ganic remains in such intercalated 

 beds will, of coui'se, fall naturally into their places in the animal 

 series ; but the insertion of the strata themselves in our tabular 

 lists can only be done, save for limited areas, by assigning undue 

 weight to artificial arrangements. It may not perhaps be neces- 

 sary to go so far as to consider the Devonian or Permian forma- 

 tions as the arctic conditions coincident with a tropical Carbonifer- 

 ous aspect of life ; but the overlap, so to speak, of jihysical con- 

 ditions, which it seems impossible to evade, admits of no precise 

 limitation ; it must either be denied, or accepted along with all 

 it involves. 



But if tlie simple case, when the fossils are identical, presents so 

 many difficulties, palaeontology must, a fortiori, be still less relia- 

 ble as a lawgiver, where distant formations yield dissimilar fossils. 

 For zoology Icnows no law by which structural modifications can 

 be so classified, that their relative ages may be determined by in- 

 spection ; nay, those best qualified to speak with authority shrink 

 even from asserting a progression of types from higher to lower, 

 in time. The very theory, which sees in these modifications in- 

 cx'casing adaptation to external conditions, dejirives jialaiontology 

 of all power of jirediction apart from physical observation. The 

 important caution given by Mr. Huxley (p. 40) against the assump- 

 tion of identity of habits from similarity of form, points in the 

 same direction. Lyell ("Elements," chap, ix.) points out the diffi- 

 culties arising from difierences of contemporaneous deposits, as, 

 for instance, in tlie Levant and Red Sea, but sees no means of 

 fixing their relative age, save where they are not far apart, and 

 belong to the same province of terrestrial distribution ;■ in which 

 case, members of the common fauna and flora, accidentally pre- 

 served, might fix the relative age. A striking instance of the un- 

 certainty in dealing with organization is offered by the Miocene 

 formation. Its flora, as seen in Switzerland, finds its nearest liv- 

 ing repi-esentative in the vegetation of the Southern States, and 

 the resemblance is very strong. It must, therefore, have lived 

 down to, co-existed with, and survived as a flora, the glacial era. 

 Yet tlie most accomplished botanists vary so widely in their ojjin- 

 :. ions, that the plants are by some traced eastward, by others west- 

 t ward from America ; by others have been supposed to radiate 

 - from a centre lying between Switzerland and Western Asia. This 

 f unanimous difterence, be it noted, is found after decisions have 

 been limited to those species only, whose preservation leaves no 

 unceitainty in their identification, 

 ' The conclusion is, that these and similar difficulties will best 



