vi PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. 



ing generic distinctions, Mr. Davidson observes as probable, that as 

 we advance, and lacunes are filled up, distinctions will become more 

 and more arbitrary .... genera approximating to each other by a 

 multitude of intermediate species, some possessing the external 

 forms of one genus with certain internal characters of another, so 

 that there is much difficulty in assigning them their true place." 

 President's (De la Beche) Address, 1849. 



On the skirts of the Venetian Alps are equivalents of the creta- 

 ceous series of our country, graduating upward into " nummulitic 

 accumulations," which Sir R. Murchison refers to the age of the 

 lowest tertiary or eocene rocks. Two or three species of Gryphsea 

 are common to the rocks equivalent to the cretaceous series and the 

 nummulitic accumulations, thus zoologically connecting the secon- 

 dary with the tertiary formations. 



" From the accidental circumstance of the tertiary rocks having 

 been made known to us by the labours of such men as Cuvier and 

 Brongniart, working around such a seat of science as Paris, a desire 

 to perpetuate very marked distinctions between the cretaceous and 

 supra-cretaceous accumulations has not unnaturally been experienced." 

 A reluctance has been long experienced "at considering the accumu- 

 lations of mud, sand, gravel, calcareous, or other matter, of the one 

 time as a mere sequence of those of the other, and the breaks in this 

 sequence in particular areas as no more than other breaks in the 

 general deposits of other geological times, even in the same areas. 

 We are not to suppose that all the rivers of the world suddenly 

 ceased to transport detritus into lakes and seas; that the breakers 

 no longer wore away the coasts, or that animal and vegetable life 

 was entirely destroyed ; because we find a break in the sequence of 

 accumulations in a particular portion of the earth's surface. We 

 have now learned by the progress of our science, to account for such 

 long breaks, and among other things, that dry land cannot fail to 

 show them, when such dry land, after submergence, is covered by 

 marine deposits, and is again upraised above the water." Presi- 

 dent's (De la Heche] Address, 1849. 



5. THE LOWER SILURIAN FORMATION IS THE RECORD 

 OF AN ERA OF INVERTEBRATE ANIMALS. 



" The absence of even the lowest of the vertebrata in the inferior 

 Silurian rocks, an absence which is total, so far as can be inferred 

 from the researches of geologists in all parts of the world, gives 

 them a true Protozoic character ; and this condition of things was 

 mentioned by the author as a strong reason for concluding, that the 

 epoch in question was the earliest in which animal life was deve- 

 loped." Abstract of a Paper by Sir B. Murchison: Report 

 Brit. Assoc. 1844 (p. 54). 



" The most assiduous researches in various regions where 



