1821.] Mr. Weaver on Floetz Formations. 355 



Mansfield, being imbedded, in no certain order, among the other 

 beds of sandstone and clay. But in the forest of Thuringia, M. 

 Heim observes, that it occupies the central portion of the strata, 

 while the argillaceous or calcareous varieties are found toward 

 the exterior, where they are confined by the clay and concomi- 

 tant beds that intervene, on either side, between the sandstone 

 and the lower and upper limestone formations. 



The calcareous sandstone forms a substance, of a character 

 intermediate between sandstone and roestone, usually appearing 

 in beds from a half to one foot thick, the interior of which is com- 

 monly dark bluish-grey, passing toward the exterior into smoke- 

 grey. The darker varieties consist of an intimate mixture of 

 lime and silex, hard and firm, in which single grains of quartz are 

 seldom discernible ; the lighter striped varieties are distinctly 

 sandy, or they have a small fine-grained sparry texture. It is 

 seldom porous, but when in that state, it has little cement, con- 

 sisting of minute white grains of quartz. The calcareous sand- 

 stone, or siliceous limestone, passes usually into roestone. 



Roestone. (Roggenstein.) — This substance varies considera- 

 bly in the size, form, and connexion of the grains; the structure 

 of which is sometimes compact splintery, sometimes concentric 

 lamellar, sometimes foliated granular, and commonly of a smoke 

 or dark- grey, brownish-red, or reddish-brown colour. The grains 

 are found from the size of cherrystones to that of peas, hemp, 

 and millet seeds, and even much finer. The coarser grains are 

 met with closely adhering to each other, with little appearance 

 of a connecting medium, or immersed, in a more or less crowded 

 state, in a base of highly indurated clay or marl, mostly of a grey 

 or reddish colour ; or they appear singly in a sandy or marly 

 base. The grains have a rough, uneven, or a smooth surface ; 

 being in the last case usually white, and composed of concentric 

 lamellar concretions. Another variety of the finer-grained con- 

 sists of grey or brown, round or oval, grains, with a foliated 

 granular texture, lodged in a milk-white base, of a similar 

 structure. 



As the grains become smaller and gradually diffused in the 

 substance of the base, the hardness and tenacity of the stone are 

 proportionably increased ; so that at length the roestone passes 

 sometimes into a coarse or fine splintery rock, a quartzy com- 

 pact limestone, or horn-marl. And, generally sneaking, the 

 gradations are very numerous, by which it passes into sandstone, 

 marl, compact limestone, hornstone, and even into sandstone. 

 The gradation into sandstone occurs in particular in the finer- 



f rained white, or brownish-red sandstone, which contains minute 

 rown grains of roestone. Sometimes also both the roestone 

 and calcareous sandstone pass into a substance nearly resem- 

 bling sparry iron ore ; and in the clay and sandstone quarries 

 near Sangerhausen is a considerable bed of oohtic sparry iron 

 ore, the grains of which are of the size of peas, with a hair o 



2 a2 



