298 PALAEONTOLOGY. 



it naturally leads us into an investigation of the operations that must 

 have taken place on the surface of this globe ; and which also, so far as 

 the extraneous fossils go, leads to the formation of native or mineral 

 fossils. But it is to be understood that this investigation has nothing 

 to do with the original formation of the earth itself; for that must have 

 been prior to the formation of the extraneous fossil, which has only 

 a connexion with the changes on the surface ; therefore, as in the 

 fossils, our mode of reasoning on this subject maybe termed retrograde ; 

 it is supposing from the state of the earth now, what must have taken 

 place formerly ; for we are obliged to take the facts, and guess at their 

 cause ; their history, prior to their discovery, being entirely unknown, 

 and few relative circumstances, leading to it, being almost left wholly to 

 conjecture; for we have few intermediate circumstances leading from 

 one to the other ; the distance of time between cause and eifect is too 

 long for observation, and history gives us but little assistance, hardly 

 a hint. 



" In this investigation we are obliged to search after the causes of 

 operations from effects completely performed ; but as these may be made 

 out at some future period, their history becomes a kind of mark for 

 future ages to judge by, and will be the means of correcting the errors 

 we now naturally run into ; all of which we should have been unable to 

 consider, if we had not the preserved parts of sea-animals, each in a 

 great degree explaining the other. 



" The fossils of sea-animals inform us of the change of place in the 

 waters, otherwise we could not have supposed it; just as we would 

 trace the remains of former actions in any country by the monuments 

 left, judging of past by present." 



" As this is a subject connected with, or makes a part of, the Natural 

 History of Vegetables and Animals, it has by me been occasion- 

 ally one of my pursuits, with a view to match the fossil with the 

 recent animal, and see how the present corresponded with the past ; in 

 which time I have, with the assistance of my friends, made a con- 

 siderable collection 1 , and have arranged them according to a system 

 agreeing with the recent." — Pp. i & ii. 



Hunter, in defining 'Extraneous Fossils,' does not limit them to 'Parts 

 of Animals and Vegetables found buried in the earth,' but extends the 

 term to 'impressions,' 'casts,' and 'moulds of such' — a class of evi- 

 dences the value of which has subsequently been fully appreciated, and 

 which has been found to include not only impressions made by the dead 

 organisms, but those left by the footsteps of living animals, as well as 



1 [See p. 295.] 



