MAQNESIAN LIMESTONE. 



MAGNESIAN LIMESTONE. 



/fydromaynnile u a name given to an earthy white pulverulent 

 hydrous carbonate of magnesia found at Hobokcn, New Jersey, North 

 America. 



Roraif of Maynena, Boracitr, is a common form of magneaian 

 mineral. [BoHox.] 



fiilrale of Maynttia occurs in white deliquescent efflorescences, 

 Mnociatnil with nitrnte of lime, in limentone caverns. It is used in the 

 iiiMitifactiire of saltpetre. 



Poiyhalilt, n brick-red saline mineral, consists of the sulphates of 

 lime, potash, and magnesia, with 6 prr cent, of water. 



Maynnitt a a phosphate of magnesia, from Snlzberg, in Germany. 

 Mudiiitt resemble* Boravite. It occurs with the red tourmaline 

 of Siberia. 



Mag*uia Alum occurs massive, lit structure is fibrous, also com- 

 pact. Colour and streak snow-white. Lustre shining. It is found at 

 Cape Verd, in Southern Africa, where it covers the floor of a grotto to 

 the depth of six inches. Its analysis by Stromeyer gives 



Sulphate of Alumina 38-398 



Sulphate of Magnesia 10'820 



Sulphate of Manganese .... 4-597 



Chloride of Potassium 0-205 



Water 45739 



99759 



ifagnetian Pharmacolite occurs massive. Cleavage fulinted in one 

 direction. Colour dirty white, or honey-yellow. Hardness 5 to 6. 

 Brittle. Lustre waxy. Specific gravity 2'52. Found at Liingbansbyt- 

 tm in Wenneland. IU analysis by Kiihn given 



Arsenic Acid 58.52 



Lime . . . - 



Magnesia 



Protoxide of Manganese 



Iron .... 



Loss by Ignition 



23-22 

 15-68 



2-13 

 a trace. 



0-30 

 99-85 



The silicates of magnesia are an exceedingly numerous group of 

 minerals. They enter into the following : Tale, Chlorite, Serpentine, 

 Mrpkrite, Meenchaum, Schiller Spar, Pyroxene, Hornblende, Chryiolite, 

 Clxmdrodile. 



MAQNESIAN LIMESTONE, or Permian System, is the name 

 given to the rocks which immediately underlie those of the Triassic or 

 Upper or New Red-Sandstone series of England. In Russia a large 

 group of deposit* of this date exists, and is marked by distinct pecu- 

 liarities. The abundance of carbonate of magnesia is characteristic of 

 part of the series hence its name. The Magnesian Limestone rock 

 is Men to greatest perfection in England between the rivers Tyue and 

 Tees, between the rivers Wharf and Dun, and between this last river 

 and Nottingham. We mention these ports of the great line of mngne- 

 sian limestone in the north of England for the purpose of pointing 

 out some interesting differences in the composition and other characters 

 of the rock. It is in the middle part of the coun-c here indicated, 

 from north to south, that the stratification of the rock is moat 

 developed. Between the Dun and Wharf, and for some space north 

 and south of these riven, this limestone occurs in fact in two rocks 

 separated from each other by beds of red and bluish clay, with gypsum 

 (inditinguihable from some of the upper or Keuper marls of the Red- 

 Sandstone .Formation); but in the northern and southern parts this 

 difference docs not obtain. Of the two limestones thus separated the 

 upper one has but a limited extent (Smith's ' Geological Map of York- 

 shire '); the lower one in almost uninterrupted from beyond the Tyne 

 nearly to the Trent. The upper rock is about 12 yards thick ; the 

 lower one reaches 50 yards, or perhaps in some cases 1 00 yards : the 

 upper one contains almost no magnesia, and lime burnt from it is 

 extensively employed in agriculture ; the lower one is very often com- 

 posed of atomic aggregations of carbonate of lime and carbonate of 

 magnesia, and, both as stone and when burnt to lime, is more useful 

 in building. IU mode of aggregation varies extremely. ' In many 

 situation* (Thorp Arch, in Yorkshire) it is a soft powdery stone, 

 traversed nevertheless by veins of calcareous spar ; about Tadcaater, 

 and generally between the Nid and the Dun, it is a firm though hardly 

 compact rock, often traversed by sparry veins and full of irregular 

 crystallised cavities. The crystals are generally carbonate of lime, 

 sometimes mixed with oxide of iron. In a few cases sulphate of 

 barytas appear* in the form of veins dividing this rook, as at Huddle- 

 ston, n<-ar Ferrybridge, Ac. Still less commonly thin veins of car- 

 bonate of copper (sometimes apparently epigene, on sulphuret) line 

 the joints of the rock about Newton Kymc, near Tadcaster, and in 

 other places. 



Some of the beat building-stone of this description is dug in the 

 quarries of Huddleston, Broadsworth, and Warmsworth, and it i 

 generally really or nearly an atomic combination of carbonate of lime 

 and carbonate of magnesia, a fact determined by the late Dr. Henry 

 of Mancherter. 



A further state of arrangement of the materials of this rock is 

 noticed in several localities between the Aire and the Dun, where the 

 rocks assume locally and for limited areas the oolitic texture ; and, 

 finally, as one of the most valuable building-stone* in the range of the 

 msgnssitn limestone, my be signalised the white limestone of Roche 



Abbey, which in that noble ruin has stood the ravages of time better 

 than almost any freestone of the north of England. 



Farther south the grain of the rock changes; it becomes continually 

 more and more crystalline, ami from Bolsover to Nottingham the 

 magnesian limestone may be described, with little inaccuracy, as a real 

 dolomite, partially debased by small admixtures of sand. The small 

 rhomboids! crystals of this rock are very evident in specimens which 

 we collected many yean ago at Mansfield Woodhouse and near 

 Nottingham. The atone used for building the present Houses of 

 Parliament consists of the magnesian limestone from this district. 



A crystalline structure of the magnesian limestone rock is however 

 not confined to the southern portion of its range, though there it is 

 manifested in connection with very useful qualities in architecture. 

 In the county of Durham we find it exhibited in the purely calca- 

 reous rocks of Hawthorn Hive, near Easington, in the romantic, 

 contorted, and broken cliffs and pinnacles of Marsden, and in the 

 singular coralloidol quarries of Building Hill. At Marsden it is 

 curious to notice in near contrast, in the cliff, the 6exible laminated 

 limestone, and in the detached pinnacles an equally laminated rock 

 traversed by complete planes of crystalline structure. What does 

 this teach ? obviously, the important fact, that, since its deposition in 

 lamina;, the sedimentary mass of carbonate of lime has been subject 

 to a new molecular arrangement, which, predominating over the 

 original structure, has readjusted the particles and generated a new 

 structure. In the some vicinity are brecciated rocks, which seem to 

 require the hypothesis of reaggregation of fragmented portions of 

 previously-indurated magnesian limestone bed*. Thus various are the 

 aspects of the mineral aggregation of the magneaian limestone of 

 England. These divenities belong almost exclusively to the lower 

 rock, for the upper laminated non-magnesian portion is usually of a 

 uniform close texture, except in the lower beds, which are somewhat 

 cellular (and of little value to the lime-burner) at Knottingley. 



It flhould be added, that the general colour of the magnesian lime- 

 stone (lower portion) is white, yellow, rich pale-brown, or reddish, 

 while the upper rock is commonly of a gray, smoky, or purplish hue. 

 This rock is usually interstratified with thin clay partings, the lower 

 one very rarely. 



The specific gravity of magnesian limestone is usually greater than 

 that of common carbonate of lime. This however may be overlooked 

 in the usual incomplete mode of trying such experiments, unless the 

 observer makes the easy correction due to the absorption of water by 

 many of these stones. Tried in powder (for example, by Leslie's pro- 

 cess), the magnesian limestones of England betray by their Wright 

 their affinity to the dolomitic rocks of the Alps and the Eifel, though 

 the introduction of the magnesia is probably not at all due to the 

 same cause in the two cases. [DOLOMITE.] 



Professor Sedgwick, in his admirable memoir in the 'Geological 

 Transactions,' on the Magnesian Limestone, has pointed out clearly 

 the most common organic fossils of this rock. We shall only observe 

 here, that in respect of fishes (Molliuca and Zoophyta) this rock shown 

 an extreme analogy with the Carboniferous System. Its place, by 

 mineral analogies, may be rightly fixed in the Pojcilitic System ; but 

 by the affinities of organic existence it will be classed with the more 

 ancient rocks. Let any one, for example, contrast iU marine fossils, 

 whether derived from Durham, Yorkshire, or the Thuringerwald, 

 with those of the Muachelkalk ; the former are seen to be analogous 

 to forms common in the Mountain Limestone, the latter to those of 

 the Lias. In neither case is the resemblance perfect ; the species are 

 not identical, but the result above announced i unequivocal, and 

 must soon be felt in geological classification. 



The following is a list of the fossils in this formation as given in 

 Tennant's ' List of British Fossils ' : 



Polyparia, 



Tul>idicli<li tpinifera. 

 PtntttMa. ancepi. 

 P. fliutracea. 

 P. rnmoia. 

 P. virytUacea, 



Crinoidea. 



Encriniu ramotui. 



Jirachiopoda. 

 Terebraiula dongata. 

 T. in flata. 

 T. Schlotkeimii. 

 Atrypa pectinifera, 

 Spirifer undultUut. 

 ~ 



S. rriitatia. 

 Productta horridut. 

 /'. M vrruiCHMU. 

 1'. xpinifcrui. 

 f,inyula Mytiloida. 



Itimyaria. 

 AUoruma elegant. 



ScJiizodtu obncurtu. 

 8. paralltliu. 

 S. truntattu. 

 S. rotundattu. 

 S. parrui. 



S. UH'fa'lU. 



*. pvMlut. 

 S. mini tn in. 

 tfucvla rinti. 

 A rca tumiila. 

 M/tiilta Hcnmtnalut. 

 M. teptifenu. 

 Modiola coitala. 



Monomyaria. 



A ricula ipeluncularia. 

 A. keratophaga. 

 A . antique. 

 A. injlata. 

 A. Xinntyi. 

 A. ditcort. 

 A. Gervillia. 

 Peclen putitlv*. 

 Ottrea, puiilln. 



