internal Structure of the Magnesian Limestone. 75 



hypothesis at defiance : for the true stratification may be discovered in places 

 where the Hne of its direction bears no relation whatsoever to the plane which 

 separates the sandstone from the limestone. (See Plate VI. fig-s, 2. & 3.) The 

 examples to which I have referred probably form merely local exceptions to 

 the more general rule. If, however, future observations should prove them to 

 be more numerous, it will then be necessary to make a slight modification of 

 the classification which is proposed, and to remove the formation here de- 

 scribed from the group composed of the higher portions of the new red sand- 

 stone series. In that case it must be placed in a class by itself; for on no 

 account can it be admitted into the carboniferous order without violatino- the 

 best rules of geological arrangement*. 



§ 2. A deposit of Marl-Slate, and of thin-bedded and neurit/ compact 



Limestone, ^c. 8^c. 



On passing over the edges of the several deposits already described, and 

 mounting to the lower portions of the terrace of magnesian limestone it 

 might, after a partial examination, appear a hopeless task to attempt to reduce 

 the several calcareous beds to any natural order. The very same beds at short 

 distances from each other, and sometimes even in the same quarry, are cry- 

 stalline, earthy, compact, or cellular ; perpetually changing their mode of 

 aggregation in such a way as almost to baffle description. In the midst of 

 this confusion there are, however, certain beds which preserve a considerable 

 uniformity of character ; and which, though by no means co-extensive with 

 the formation of magnesian limestone, wherever they do appear are generally 

 found in the same j)ortion of it. Such are the beds of marl-slate and thin- 

 bedded compact limestone, which in several parts of the range through the 

 county of Durham, and in some parts of Yorkshire, rest immediately upon 

 the lower red sandstone. In placing them in a separate group, I have not 

 therefore adopted an arbitrary subdivision for the mere purpose of bringing 



* In an excellent memoir by M. L. Elie do Beaumont on tlie secondary formations of (he 

 Vosges (whicii did not appear til! after tliis paper was written), a deposit is described under the 

 name of gres dcs Fosges, which, both in structure and position, agrees very exactly with tlie 

 lower red sandstone. It deserves remark, that this deposit, like the formation described above, 

 appears in several places to have undergone considerable degradation before the existence of some 

 of the higher groups of the new red sandstone series. " Dans beaiicoup de localites, le depot 

 de gres qui, sans aucim doiite, fait partie du gres bigarre, parait reposer a stratification 

 discordante sur le gres des Vosges, et semble n'' avoir commence a se deposer qu^apres que la 

 surface de ce dernier avail siibi des degradations considerables.^' — Observations Geologiqucs 

 sur quelques Terrains Socondaires du Systeme des Vosges, p. 54 — 55. 



After the new analogies supplied by the details of this paper, it a|)pears at least highly pro- 

 bable that the whole of the gres des Vosges is the equivalent of the luxccr red sandstone, and 

 that no part of it (as has been conjectured) is contemporaneous with our magnesian limestone. 



l2 



