282 
SILUEIA. 
[Chap. XI. 
shire. In Ireland the Middle Devonian, or the limestone of Devon- 
shire and the Eifel, which, from its fossiliferons structure, gives the 
dominant character of the system, is wanting, as indicated by the pre- 
ceding diagram, p. 281 ; for the lower slaty grits (d) are unconformably 
overlain by sheets of red sandstone (/), more or less horizontal, which 
overlap the edges of the older rock. We have in this fact, the great hiatus 
which occurs between d and /, the most decisive proof that the central por- 
tion of the Devonian or Old Red system has been omitted in Ireland. 
In Ireland the lowest Carboniferous rocks, which are slaty, and are 
known as the Carboniferous Slates, stand precisely in the same geological 
position, in reference to the strata beneath and above them, as the Lower 
Calciferous Sandstone of Scotland, of which Edinburgh is built, and the 
Lower Limestone-shale of England. They are only mentioned here to indi- 
cate their natural position in the general order of succession, and to show 
how completely I dissent from an opinion recently expressed by Mr. J. 
B. Jukes, that these Carboniferous Slates of Ireland occupy the lower 
part of that 'which is known to be the Devonian formation of North 
Devon, as already described above. Generalizing from this assumption, 
Mr. Jukes infers that the great series which all geologists who have ex- 
amined the tract in the south-west of England call Devonian is nothing but 
the equivalent of the lowest member of the Carboniferous rocks of Ireland. 
He therefore infers that the belief of all other geologists in Europe and 
America must be overthrown, and the so-called Devonian system merged 
in the Carboniferous as being superior to the Old Eed Sandstone *. 
The Carboniferous Slates of Ireland, which contain exclusively Carbo- 
niferous fossils and no Devonian forms, will be again briefly mentioned 
in the next Chapter. They have only been here alluded to in defending 
the truthfulness of the classification adopted, and the true position oc- 
cupied by the Devonian rocks in the general order of the palaeozoic depo- 
sits, which has been for the first time impugned by a geologist of repute f , 
but to whom I reply by indicating that the order of the very rocks in Ire- 
land to which he refers supports the view which I entertain, in common 
with all my other cotemporaries, as far as I know. 
Let me here, also, observe, that on the Continent of Europe there 
are many large accumulations of similar non-fossiliferous rocks with an 
equally antique aspect, which occupy the same place in the geological 
series. Thus, amidst the slaty and siliceous Devonian rocks of Germany, 
there are vast thicknesses of strata wherein few or no organic remains 
have yet been detected ; their age being only made known by their inter- 
mediate place in the series, and rarely by a calcareous fossil-bearing 
course. 
* Mr. Jukes, in his paper on this subject (see to reconcile the facts with his own theory. (See 
Quart. Journ. Geol. Soc. vol. xxii. p. 321), admits p. 276 &c. ante, in which it is shown that the de- 
that the order of succession in the rocks of North cisive Devonian fossils in these rocks are corn- 
Devon as given by Professor Sedgwick and my- pletely subversive of Mr. Jukes's 'Carboniferous' 
Helf is correct, and therefore is obliged to imagine view.) 
a great longitudinal fault of gigantic dimensions 
