THE NEW RED SANDSTONE SYSTEM. 71 1 



Magnesian limestone. This part of the formation is well developed in a continuous 

 band, extending from the Tyne southwards through Yorkshire, and descending into the 

 counties of Derby and Nottingham. Towards the northern and southern extremities the 

 strata rise into a series of round-topped hills ; but the centre sinks to the general level of 

 the country. The appearance of stratification is very distinct, and several varieties of 

 structure occur, some beds being granular, others imperfectly crystalline, and others 

 cellular. In the latter variety, abundant in the county of Durham, where it bears the 

 name of the honeycomb limestone, and answers to the rauwacke of Germany, the cells 

 are lined with crystallised carbonate of lime. The rock, as its name imports, is a com- 

 pound of the carbonate of lime and the carbonate of magnesia, in various proportions ; 

 but calcareous beds are common, in which there is little or no admixture of magnesia with 

 the lime. It forms one of our most durable building stones, and has been largely used 

 in the construction of some of our finest edifices, as York-minster and Westminster 

 Hall, which have admirably withstood the wear and tear of the atmosphere. It is now 

 employed in the erection of the new houses of Parliament, derived from the Bolsover 

 quarries in Derbyshire. An analysis of the stone of York-minster gives 



Carbonic acid - - 47 '00 Magnesia - - - 19 '36 



Lime ; i <* .;-;, ' 83*24 | Iron and clay i - -m-,, . '40 100 



The stone of Westminster Hall contains about 2 per cent, less of magnesia, but the 

 proportion is often far greater, amounting to more than 50 per cent. Magnesia in minute 

 quantities is very extensively distributed ; it occurs more largely in the mountain lime- 

 stone, oolites, and chalk ; but is only found in such abundance in the limestone of this 

 system as to become a characteristic. The two constituents of the rock, the carbonates of 

 lime and magnesia, some suppose to have been deposited contemporaneously ; but Von 

 Buch considers the magnesian limestone to be a metamorphic change of common limestone, 

 effected by the disengagement of vapours containing magnesia from plutonic masses. 

 But it has been justly remarked, that, according to this theory, we ought to expect all 

 limestones to become magnesian in the neighbourhood of igneous rocks, which is far from 

 being the case. 



Gypsum. This sulphate of lime, one species of which is commonly known under the 

 name of alabaster, frequently appears in association with the red marls and sandstones 

 of the upper part of the system. It occurs in detached nodules of fibrous structure, in 

 horizontal seams equally fibrous, varying from one to three inches in thickness, and in 

 amorphous granular masses capable of being worked into columns. The red marly 

 banks of the Trent exhibit beautifully white and translucent seams of gypsum ; and at 

 Chellaston, not far from the borders of the river, it appears in a granular mass, from 

 which the beautiful pillars at Kedleston Hall, near Derby, were wrought. Its origin has 

 been referred by some to segregation from the surrounding sedimentary matter ; but its 

 common connection with rock-salt, wherever the latter mineral is found, is considered 

 by others as indicating its formation from the same cause. 



Rock-salt. The mineral, chloride of sodium, is not peculiar to the series of deposits 

 under notice, for salt springs occur in the coal-measures, and in strata belonging to the 

 modern volcanic period j and salt is procured from the chalk and oolite systems. Former 

 writers, therefore, were too hasty in referring the production of all the saliferous deposits 

 upon the face of the globe to the geological era of the new red sandstone. Still, saline 

 strata clear, white cubically crystallised masses of salt, and brine springs issuing from 

 such rocks are so remarkable and frequent in it, as to be justly regarded one of its 

 distinguishing features, and hence the common application of the term saliferous to the 

 system itself. By far the finest example of rock-salt in Europe, on account of its position 

 at the surface, is at Cardona, a small town in the interior of Catalonia, sixteen leagues 



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