THE LAW OF EVOLUTION CONTINUED. 349 



All inferences drawn from such scattered facts as 

 we find, must thus be extremely questionable. If, 

 looking at the general aspect of evidence, a progressionist 

 argues that the earliest known vertebrate remains are those 

 of Fishes, which are the most homogeneous of the verte- 

 brata; that Reptiles, which are more heterogeneous, are 

 later; and that later still, and more heterogeneous still, are 

 Mammals and Birds; it may be replied that the Palaeozoic 

 deposits, not being estuary deposits, are not likely to con- 

 tain the remains of terrestrial vertebrata, which may never- 

 theless have existed at that era. The same answer may be 

 made to the argument that the vertebrate fauna of the 

 Palaeozoic period, consisting so far as we know, entirely of 

 Fishes, was less heterogeneous than the modern vertebrate 

 fauna, which includes Reptiles, Birds and Mammals, of 

 multitudinous genera; or the uniformitarian may contend 

 with great show of truth, that this appearance of higher 

 and more varied forms in later geologic eras, was due to 

 progressive immigration — that a continent slowly upheaved 

 from the ocean at a point remote from pre-existing conti- 

 nents, would necessarily be peopled from them in a suc- 

 cession like that which our strata display. At the 

 same time the counter-arguments may be proved equally in- 

 conclusive. When, to show that there cannot have been a 

 continuous evolution of the more homogeneous organic 

 forms into the more heterogeneous ones, the uniformitarian 

 points to the breaks that occur in the succession of these 

 forms; there is the sufficient answer that current geological 

 changes show us why such breaks must occur, and why, by 

 subsidences and elevations of large area, there must be pro- 

 duced such marked breaks as those which divide the three 

 great geologic epochs. Or again, if the opponent of the de- 

 velopment hypothesis cites the facts set forth by Professor 

 Huxley in his lecture on " Persistent Types " — if he points 

 out that " of some two hundred known orders of plants, not 

 one is exclusively fossil/ ' while " among animals, there is 



