MAGNESIAN LIMESTONE. 



MAGNOLIA. 



699 



Gasteropoda. 

 Nalica minima. 

 Pleurotomaria carinata. 

 P. nodulosa. 

 Turbo Mancunientit. 

 T. minutus. 



Jfacroclteilut symmetrical. 

 Loxonema nufifcra. 

 L. Vrii. 

 Rissoa puiilla. 

 11. Leigkii. 

 11. rninulissima. 

 K. Giltsoni. 

 R. obtusa. 



Pisco. 

 Palceonitcut comlui. 



P. elegans. 



P. glaphyrus. 



P. longissimus. 



P. macrophthalmut. 



Platysomus macrurus. 



P. panw. 



P. striatus. 



Acrolepis Sedgwicki. 



Pygopterus mandibularis. 



Cailacantkus granulatui. 



Reptilia. 



Palteosauna Cylindrodon. 

 P. Platyodm. 

 Tkecodontosaurua antiquus. 



The Magnesian Limestone assumes a variety of forms simulating 

 those arising from organic causes. Amongst these are the round 

 masses which are found on the coast of Durham. At a distance these 

 masses look like cannon balls, and the rock ii which they occur 

 has obtained the name of Cannon-Ball Limestoue. In many parts 

 the rock has a pisiform or oolitic appearance, from being composed 

 of small round bodies. These little masses, when submitted to the 

 microscope, afford no evidence of having been deposited from organic 

 causes. They are evidently concretionary, and have probably been 

 slowly deposited from a solution of the magnesia and lime of which 

 they are composed. 



" In the quarries of Askern and Campsall, round or oval projections 

 are seen, which vary from a pin's head to several feet in circumference. 

 The layers of which they are composed are continuous with those of 

 the limestone, and seem to be formed by some foreign substance 

 serving as a nucleus upon which the limestone is deposited layer after 

 layer ; in some cases, the nucleus may be formed by the escape of 

 carbonic acid or other gas, for I have frequently observed that the 

 protuberance is hollow within. 



" There is another class of bodies which have a conoidal form, the 

 base being always uppermost ; their size ranges from that of a pea 

 to that of a large pear ; they are not continuous with the layers of 

 the limestone, but lie in distinct cavities, from which they may be 

 removed almost entire, by a blow of the hammer. The cavities in 

 which these bodies are found have probably been at first made by the 

 rotatory action given by running water to a small stone, or other 

 substance, whilst the limestone was forming, a fresh deposit having 

 afterwards taken place from the water : cavities of this kind may be 

 frequently seen in streams running over loose sand, or other matter. 



" Another striking feature in the physical character of the magne- 

 sian limestone is, the existence, in some places, of an immense number 

 of cavities, which are frequently lined with beautiful crystals of 

 carbonate of lime ; some of these cavities are very small, as in the 

 oolitic limestones ; they are to be seen at Smeatou several feet square : 

 the greater proportion of them contain crystals, and vary in size from 

 a marble to an orange. Some geologists imagine that these cavities 

 have been formed by the deposition of the rock upon gelatinous 

 animal bodies, which, being gradually removed by decomposition, have 

 left their- mould or cast behind ; others suppose that they have 

 originated from the escape of gaseous matter, which, whilst the rock 

 was hardening, was incapable of rising to the surface. By the subse- 

 quent passing of water, charged with carbonic acid, through these 

 cavities, many of them would become enlarged by the dissolving 

 power of this gas over the limestone. 



" The productions called Stalactites and Stalagmites are often found 

 in the dislocated and over-hanging portions of Maguesiau Limestone ; 

 the former are long, depending like icicles ; the latter are flat, and 

 thinly extended over the surface of the rock. At Askern many beauti- 

 ful specimens of stalagmites have been taken from the quarry." 

 (Lankester, ' History of Askern.') 



The Magneaian Limestone series may be traced in the north of 

 France and in Burgundy, but is most fully developed at Mansfield in 

 the Thuringian Forest, in the district of the Hans, and in Franconia. 

 Throughout the south of France it appears to have no representative, 

 and is most likely altogether absent. When most perfectly expanded, 

 the whole series is divisible into two groups, the lower one for the 

 most part argillaceous, and the upper calcareous, and the series then 

 rests immediately upon the conglomerates of the Rothe-todte- 

 liegende. 



The upper or calcareous portion in Germany is called Zechstein, 

 and is chiefly a compact limestone, but the highest beds are marly 

 consisting of, 1st, a grayish,' bluish, or greenish clay, called Letten, 

 often containing rolled fragments of dolomite and crystals of gypsum. 

 This reposes on a fetid limestone called Stinkstein, which is a compact 

 or granulated rock of a blackish-brown or greenish colour, and ex- 

 tremely bituminous, giving out an offensive odour when struck or 

 rubbed. The lower bed of the Zechstein is called Rauwack<5, and 

 consists of a hard lint cellular magnesian limestone, abounding in 

 long, irregular, and narrow cavities, which are most numerous where 

 the bed attains a considerable thickness, but are almost obliterated in 



the thinner and more compact portions. The whole thickness of the 



Zechstein is rarely more than 20 or 30 yards. 



Of the schistose beds, which form the base of the Magnesian Lime- 

 stone series, the lowest is sandy, and forms a kind of transition from 

 the underlying sandstones. It is of no great thickness, apd is suc- 

 ceeded by a bituminous band, remarkable for great uniformity both 

 of mineral character and fossil contents, being traceable over a con- 

 siderable district in Germany, and forming an excellent geological 

 horizon for an extent of at least 250 miles. According to M. 

 D'Aubuisson one-tenth part of the mass of this bed consists of . 

 bitumen aud carbon ; and although not more than a foot in thickness 

 it contains so considerable a quantity of iron and argentiferous copper 

 pyrites as to be worth working as au ore, whence it has received the 

 name of Kupfer Schiefer, or Copper-Slate. 



The lowest bed of the magnesian limestone group is called, from its 

 lithological character and relative geological position, the Lower New 

 Red-Sandstone ; but it might very fairly be associated with the upper 

 coal-measures, for it contains numerous remains of extinct vegetables 

 not to be distinguished from species found throughout the carboni- 

 ferous system. It differs somewhat however from the coal-grits in 

 mineral composition, being more discoloured with oxide of iron, besides 

 being chiefly made up of conglomerate, in which quartz and decom- 

 posed granite abound. This conglomerate, although in its lower 

 portion exceedingly coarse, passes upwards into a, fiue-grained sand- 

 stone, and so by finer sands mixed with marl shows a gradual transition 

 to the upper and marly beds. Beds of freestone are sometimes but 

 rarely found alternating with the fine sands and clays of this division; 

 and the mass is altogether very irregular both in thickness and extent, 

 appearing to have presented an uneven surface at tho commencement 

 of the deposit of the more recent magnesian limestones, and in some 

 places to have undergone considerable degradation before those beds 

 were superimposed. The irregularity thus described as affecting the 

 lower strata must have been owing, in all probability, to subterranean 

 movements disturbing the bed of ihe ocean during the period of their 

 deposition. The marls associated with the fossiliferous bands in the 

 county of Durham are also sometimes bituminous, and traces of 

 bitumen occur in thin bedded compact limestones of the same 

 geological date. 



The lower new red-sandstone, or Rothe-todte-liegende, as observed 

 in Germany, is perfectly similar in almost all respects to the contem- 

 poraneous beds in our own country, being made up of coarse conglo- 

 merates alternating with marls and shaly beds, the conglomerates 

 being generally composed of fragments of the neighbouring crystalline 

 rocks, cemented by a fine ferruginous and sometimes argillaceous 

 sandstone. In France this deposit is exhibited wrapping round the 

 old rocks which form the central axis of the Vosges. It consists of a 

 coarse incoherent sandstone, generally of a red but sometimes of a 

 bluish-gray colour, alternating with shaly and micaceous marls, the 

 whole formation being extremely variable both in its mineral character 

 and in the extent of its development. It passes insensibly into the 

 upper beds called the ' Gres des Vosges/ or Vosges Sandstone, there 

 Deing no intermediate bed of magnesian limestone. 



The Permian system of Russia exactly corresponds to the magnesiar 

 imestone and lower new red-sandstone of our own country; but it lias 

 Deen judged advisable to give a distiuct name to the continental group, 

 and the district in which the rocks are most perfectly exhibited being 

 ncluded in the ancient kingdom of Permia, that name has been selected 

 or reasons similar to those which induced Sir R. Murchison on a former 

 occasion to apply the term Silurian Formation to a group typically 

 exhibited in the region of the ancient Siluri. The Permian district 

 extends for about 700 miles from north to south along the western or 

 European flanks of the Ural chain, and for nearly 400 miles between 

 ;hose mountains and the river Volga. The strata within this area 

 are described as lying in an enormous trough of carboniferous lime- 

 stone, and though occasionally thrown into anticlinal axes of some 

 ength, are often traceable for great distances without any break or 

 nterruption of the sequence. The Permian rocks of Russia consist of 

 a great number of distinct strata of very varied lithological character. 

 They are composed for the most part of white limestones with gypsum 

 find rock-salt, of red and green gritstones with shales and occasionally 

 copper-ore, and of magnesian limestones, marlstones, conglomerates, 

 fcc. The whole series is fossiliferous, and contains the remains of 

 extinct animals and vegetables, greatly resembling those of the car- 

 xmiferous period. In the Russian beds also there have been discovered 

 eptilian remains like those of the Bristol magnesian conglomerate, 

 ind fish identical with the species from Durham and from Mansfeld in 

 he Thuringian forest. 



(Sedgwick, in Geological Transactions; Smith, Geological Map of 

 forks/lire, &c. ; notices of contemporaneous deposits in the midland 

 ind southern counties of England occur in Murchison'a Silurian 

 System ; Conybeare and Phillips, Geology of England and Wales, &c. ; 

 Ansted, Elementary Course of Geology.) 



MAGNESITE. [MAGNESIA.] , 



MAGNET, NATIVE. [IRON.] 



MAGNO'LIA, a genus of Plants named in honour of Piert'e Magnol, 



who was professor of medicine and prefect of the botanic garden of 



rfontpellier. He was born in 1638, and died in 1715. Ho gave an 



ccouut of the plants growing wild about Montpellier, in a work 



