1821.] Mr. Weaver on Floetz Formations. 345 



with streaks of brown ; partly friable, partly solid, as compounded 

 of rough sandy particles, or of crystalline ; texture, more or less 

 distinctly slaty. Also brecciated; and amygdaloidal with grains 

 of carbonate of lime and quartz. Contains sometimes rounded 

 and angular portions of marl, blue clay marl, and nodules of 

 rauhwacke ; besides aphrite in grains, membranes, or flocculent. 

 Rauhstein commonly reposes on rauhwacke or zechstein, beino- 

 covered by asche or swinestone; but it is sometimes found in 

 single masses or layers, imbedded in rauhwacke or in asche, 

 and also in blue clay marl with nodules of gypsum. A consider- 

 able proportion of the rauhkalk of the forest of Thuringia appears 

 to be the same substance. 



Asche, or earthy swinestone, seems in a great measure confined 

 to Mansfeld and the adjoining parts of Thuringia. It is com- 

 posed of fine sandy or pulverulent particles, which in its native 

 seat are compacted to a certain degree ; but on exposure become 

 friable, and fall into a fine dust on the slightest touch. Very 

 fetid, and effervesces violently with acids.* It passes on the 

 one hand into black clay marl, and on the other into swinestone. 

 Minute dusty particles of mica and calcareous spar are usually 

 intermixed with it; also spots and streaks of iron ochre. 

 Aphrite, earthy, foliated, and slaty, occurs in it in large round 

 masses, exceeding the head in size, or in numerous layers from 

 one to six inches in thickness, also disseminated. Beds of clay 

 marl, and thin layers of quartz sand, appear also in it. The 

 asche commonly forms a bed, from three to ten feet thick, lying 

 between rauhwacke and swinestone, but it is sometimes three 

 four, or eight fathoms in thickness, yet then never pure. Some- 

 times also it lies between zechstein and rauhwacke ; and, more 

 rarely, it appears in slight beds, alternating with gypsum and 

 swinestone. When covered by gypsum, it contains spheroidal 

 masses from one to one and a half foot in diameter, composed of 

 concentric alternating layers of gypsum, swinestone, rauhstein, 

 or asche, with disseminated aphrite. It is free from petrifac- 

 tions. 



Swinestone. — This substance occurs in different states : in 

 pure strata ; as a conglomerate ; or in union with gypsum. 

 The last will be considered under the head of gypsum. 



The stratified swinestone is found varying in thickness from 

 three feet to 20 fathoms. Brownish-black, or bluish-grey, with 

 black cloudy spots ; thin slaty, passing into compact, or imper- 

 fectly foliated. Dendritic delineations are common in it. Stra- 

 tification seldom permanently regular, being subject to undu- 

 lated, or sudden angular, inflexions ; the strata sometimes 

 forming also circular concentric groups. Contains incidentally 

 nodular masses of drusy sandstone, and also cavities, a few 



• In composition and general character, asche seems somewhat analogous to the rot- 

 hu of Derbyshire. The geological position of the latter, however, is very different, 

 being found in the iirst iloeu or carboniferous limestone. 



