.1866.] JUKES OLD RED SANDSTONE AND DETONIAN. 367 



or tacit reference to sections in the first instance, showing the 

 stratigraphical relations of the beds. 



It may be reserved for some future palaeontologists to treat fos- 

 sils independently, and show, from their biological relations only, 

 the necessary laws which must have regulated their appearance in 

 time ; but I am not aware of any one having even attempted this 

 task as yet. 



To take an extreme ease at once, the family of the Oraptolitidce 

 for instance : if any geologist now find in any rock a fragment of 

 a Graptolite, he refers the age of that rock to one of the Lower 

 Palaeozoic periods with the utmost confidence, and in no known in- 

 stance would he be wrong in so doing. But he does so, not because 

 of anything in the organic structure of the fossil, but because no 

 one ever yet did find a Graptolite in any rock which could be 

 shown stratigraphically to belong to the Upper Palaeozoic or any 

 higher part of the series. No palaeontologist, so far as I am aware, 

 could show a merely biological reason why the Graptolites might 

 not have existed during the Secondary or Tertiary epochs. Or 

 suppose that no shells belonging to the genus Producta had ever 

 yet been seen, could any one on the first discovery of a Producta 

 have decided on its age without any reference to the stratigraphi- 

 cal position of the bed in which it was found ? Even if he had 

 guessed, from its biological relations to other Palaeozoic Brachiopods, 

 that the shell was itself of Palaeozoic age, still he must have based 

 his conclusion on the fact that those other Brachiopods had hitherto 

 been found only in beds which were shown to be of Palaeozoic age 

 by their stratigraphical position. 



The very value of the doctrine of the chronological significance 

 of organic remains, and the constant use made of it by geologists, 

 seem sometimes to have caused them to forget that the significance 

 is a secondary and derivative one only, depending, either directly or 

 indirectly, on the stratigraphical succession of the beds in which the 

 fossils are to be found, and upon that alone. 



The peculiar Devonian species and genera of fossils, therefore, have 

 no definite value in themselves as fixing the exact place in the series 

 of the rocks in which they occur, until the place of those rocks has 

 somewhere been determined by stratigraphical evidence. Those 

 rocks have of late years been held to occupy the same place in the 

 series as the Old Eed Sandstone, or to lie between the top of the 

 Upper Silurian and the base of the Carboniferous Limestone ; but 

 where, in England or in Western Europe, is the section that shows 

 a distinct stratigraphical succession, with fully developed Upper 

 Silurian rocks below, and fully- developed Carboniferous Limestone 

 above, and a series of Devonian slates and limestones and their 

 peculiar fossils between ? There is no such section ; but if such had 

 been the order of nature, surely we should by this time have some- 

 where found a section to prove it. 



But the case is even simpler and stronger than that, for not 

 only is there no section exposing the three formations in regular 

 succession, but I have yet to learn the place where a fully-deve- 



