304 PALAEONTOLOGY". 



Thus Hook, in. 1668, writes: — "However trivial a thing a rotten 

 shell may appear to some, yet these monuments of nature are more 

 certain tokens of antiquity than coins or medals, since the best of those 



may be counterfeited or made by art and design and though it must 



be granted that it is very difficult to read such records of nature, and 

 to raise a chronology out of them, and to state the intervals of the time 

 wherein such or such catastrophes and mutations have happened, yet it 

 is not impossible." 



The same figure or simile occurs a hundred years later in Berg- 

 mann's ' Meditationes de systemate Fossilium naturali,' 8vo, Oxon, 

 1788, in which that great chemist, for his time, writes, " Horum con- 

 templatio multiplicem habet usum. Sunt instar nummorum memo- 

 rabilium quae de prasteritis globi nostri fatis testantnr, ubi omnia silent 

 monumenta historica." 



Hunter proceeds : — " But it is to be supposed that any changes that 

 may take place are superficial, respecting the size of the globe itself; for 

 we have no reason to suppose that the materials necessary to work a 

 change are deep, such as water, and whatever it can take into solution, 

 as also airs ; for, without these two states of matter, no combination of 

 matter can take place. 



" These changes are, forming solid matter into fluid, and from fluid 

 into solid again ; and it is in this last process that tbe recent vegetable 



and animal parts are, as it were, arrested or caught Such substances 



so caught, are either preserved themselves ; their impressions, which 

 must be called a mould ; or their substitute, which is a cast : such are 



termed Extraneous Fossils, many of which retain some of their form 



after many thousand centuries.' — P. iii. 



We have already had to notice Hunter's appreciation of the true end 

 of geology and palaeontology, viz. to explain the past by what we know 

 of the present, and not to invent causes now unknown, by speculations 

 on cosmogony. How far such were from his habit of thought is shown 

 by the following : — " Any changes that may take place are superficial, 

 respecting the size of the globe itself; for we have no reason to suppose 

 that the material causes of change, such as water, are deep." 



We have here the indication of the comparatively small part of the 

 earth that can be profitably or, indeed, possibly studied according to 

 the true inductive method. The greatest depths of mines, the lowest 

 soundings yet taken of the sea, the deepest insight which any upheaval 

 or fracture of the earth's crust has hitherto permitted human eye to 

 penetrate, or human mind to frame a deduction as to the structure of 

 the earth, are extremely small in comparison with the semidiameter 

 or radius of the globe. Accordinglv the best modern geologists define 



