DEVONIAN AND OLD RED PERIOD. 155 



Many of these " fin-spines " have been preserved to us in the 

 fossil condition, and the Devonian rocks have yielded examples 

 belonging to many genera. As some of the true Sharks and 

 Dog-fishes, some of the Ganoids, and even some Bony Fishes, 

 possess similar defences, it is often a matter of some uncer- 

 tainty to what group a given spine is to be referred. One of 

 these spines, belonging to the genus Machar acanthus, from the 

 Devonian rocks of America, has been figured in a previous 

 illustration (fig. io2,/). 



In conclusion, a very few words may be said as to the 

 validity of the Devonian series as an independent system of 

 rocks, preserving in its successive strata the record of an 

 independent system of life. Some high authorities have been 

 inclined to the view that the Devonian formation has in nature 

 no actual existence, but that it is made up partly of beds 

 which should be referred to the summit of the Upper Silurian, 

 and partly of beds which properly belong to the base of the 

 Carboniferous. This view seems to have been arrived at in 

 consequence of a too exclusive study of the Devonian series 

 of the British Isles, where the physical succession is not wholly 

 clear, and where there is a striking discrepancy between the 

 organic remains of those two members of the series which are 

 known as the "Old Red 'Sandstone" and the "Devonian'"' 

 rocks proper. This discrepancy, however, is not complete ; 

 and, as we have seen, can be readily explained on the sup- 

 position that the one group of rocks presents us with the 

 shallow water and littoral deposits of the period, while in the 

 other we are introduced to the deep-sea accumulations of the 

 same period. Nor can the problem at issue be solved by an 

 appeal to the phenomena of the British area alone, be the 

 testimony of these what it may. As a matter of fact, there is 

 at present no sufficient ground for believing that there is any 

 irreconcilable discordance between the succession of rocks 

 and of life in Britain during the period which elapsed between 

 the deposition of the Upper Ludlow and the formation of the 

 Carboniferous Limestone, and the order of the same phe- 

 nomena during the same period in other regions. Some of 

 the Devonian types of life, as is the case with all great forma- 

 tions, have descended unchanged from older types ; others 

 pass upwards unchanged to the succeeding period : but the 

 fauna and flora of the Devonian period are, as a whole, quite 

 distinct from those of the preceding Silurian or the succeeding 

 Carboniferous ; and they correspond to an equally distinct 

 rock-system, which in point of time holds an intermediate 

 position between the two great groups just mentioned. As 



