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earlier Silurian seas has received, by Mr. Lee's discovery in the Church Hill 

 quarry, a greater shock than lie is willing to acknowledge. Again, looking at 

 the Ptcraspis itself (and here I speak with great diffidence, because I am only 

 slightly acquainted with the complex organisation of this class), can we on any 

 sound biological principles regard it as a fish likely to begin this class in the 

 earth's history? The Ptcraspis is a placo-ganoid allied to the sturgeon, of a 

 type altogether suggestive of transition, pointing not only forwards to an 

 advanced, but also backwards to an inferior piscine organisation. 



Now Murohison's reasoning seems to be this : — Fish remains have not 

 been found in Lower and Middle Silurian rocks ; therefore, there are none in 

 those rocks ; therefore, no fishes existed in the seas under which those rocks were 

 deposited. It appears to me, however, that three conditioi s ought to be satisfied 

 before the non-existence of any given organic form in past ages can be allowed 

 to be axiomatic : (1) that its remains must, if it lived, have been embedded in 

 the deposit then forming ; (2) that those embedded remains or traces of them 

 must have been fossilised and presei-ved ; (.3) that a fuU and complete research 

 has been made in these beds, wherever they have been deposited. Let us waive 

 the question how far these conditions, especially the first, concern the existence 

 of au--breathing Vertebrata in earlier times than is indicated by the deposits 

 where their remains have been first found, and confine ourselves to fish. At 

 first sight, it would seem self-evident that if fishes lived in a sea, their 

 exuvioe — either their teeth or some parts of the endo or exo-skeleton would 

 be imbedded in the deposit, but Professor Forbes' researches have thrown great 

 doubt upon the perfectness of the record derived from the sea-bottom with 

 respect to the marine organic life during the deposition. There are besides 

 many existing species of fish, such as the lamprey and Amphioxus, certainly 

 entitled to a place in the Vertebrate sub-kingdom, that might live in shoals in 

 any sea, die and fall to the sea-bottom, and yet wlien the sediment hardened 

 and chemical changes occurred leave no trace at all of their existence. With 

 regard also to the third condition, we European geologists, and especially disciples 

 of the unwearied Murchison, think far too highly of the incursions that have up 

 to this time been made upon the earth's crust : when Asia, Africa, and America 

 shall have been surveyed and mapi^ed as carefully as part of Europe has been, 

 then shall we be justified in laying down geological axioms or generalising 

 positively from negative evidence about the commencement of any class of organic 

 life. 



One of our greatest living naturalists has well said — " For my part, I look 

 at the geological record as a history of the world imperfectly kept and written in 

 a changing dialect ; of this history we possess the last volume alone, relating only 

 to two or three countries. Of this volume, only here and there a short chapter 

 has been preserved ; and of each page, only here and there a few lines." These 

 words show us what work Geology has still to do ; to recover another chapter or 

 page, or even a line, to decipher and interpret the hieroglyphs, these are the 

 n'^ble problems set before us : and they teach us also what should be the attitude 



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