136 THE IMPERFECTION OF 



be considered as one of its definite acquisitions. There 

 is no single point of geological time at which it can be 

 said, f at this epoch clearly all old species had passed 

 away, all kinds of life had become new.' Not only is 

 there no indication of such a break, but there is the 

 strongest evidence against any such having ever occurred. 

 In spite, however, of the completeness of the evidence 

 required for proving this single conclusion, the general 

 incompleteness and enormous deficiencies in some parts 

 of the palseontological record can be established beyond 

 dispute. We are in the position of a man who has 

 kept the title-deeds to a large estate, while almost all 

 the estate itself has been buried under the encroach- 

 ments of the sea. Here and there some old landmarks 

 may be discernible far out in the waters, showing 

 the extent of what had once been meadow and 

 woodland, farm and garden, but unable to show 

 how these were distributed, or to exhibit any of their 

 details. 



Mr. Parfitt, in his paper on ' Fossil Sponge Spicules,' 

 told the Devonshire Association last year (1870) that we 

 have evidence more or less' exact of sponges in a fossil 

 state as far back in time as the Silurian system, 

 mentioning specimens of AcantJiospongia Siluriensis, 

 Cliona antiqiia, and Cliona prisca, and stating in regard 

 to the two latter that the genus is still in our own seas. 

 He then referred to large masses of a fossil in the 

 Devonian rocks of Cornwall, believed by some to be 

 sponges, and by others to be the remains of fish. That 

 these are in reality fish-remains has, in fact, been shown 



