1821.] Mr. Weaver on Floetz Formations. 347 



reposing then immediately on zechstein ; or being separated 

 from the latter merely by a thin stripe of asche. Fhe line of 

 division between those substances and the gypsum is sometimes 

 sharp and distinct, but more commonly they pass mutually into 

 each other by a reciprocal incorporation ; and endless modifica- 

 tions thus arise from the intermixture of gypsum with swinestone, 

 asche, and rauhstein. 



In some districts, where the upper gypsum occurs in the new 

 red sandstone formation, the lower gypsum is wanting, and in its 

 place we find only pure swinestone, asche, and rauhwacke. In 

 other districts, the lower gypsum is present in great thickness, 

 and the upper gypsum is wanting. In others again, both the 

 lower and upper gypsum are wanting. And in others, both 

 these formations are present ; and, when this is the case, they 

 usually lie very near to each other, being often separated by a 

 thin bed only, composed of bluish clay marl, sandstone, asche, 

 or swinestone, varying in thickness, from a few feet to a few 

 fathoms ; and it is then often difficult to determine where the one 

 formation ends and the other begins, since it rarely happens that 

 beds, several fathoms in thickness, are interposed between them. 



In the Hartz, the lower gypsum always occupies a position 

 between rauhwacke and swinestone. In the forest ofThuringia, 

 e. g. in Ilmenau and Altenstein, it lies between beds of swine- 

 stone, which are succeeded by subjacent asche and rauhwacke. 



Its thickness varies in different quarters. In Mansfeld and 

 Sangerhausen, it is usually from 12 to 24 fathoms ; but in the 

 former county it extends sometimes to 35 fathoms. In the 

 Circle of the Saale, from four to six fathoms. On the eastern 

 and northern sides of the Hartz, it is much interrupted, occur- 

 ring only in single hillocks, seldom exceeding two fathoms in 

 thickness ; so also in Lower Saxony ; but on the southern side 

 of the Hartz, its thickness varies from four to 12, up to 35 

 fathoms ; while in the forest ofThuringia, it is found from 35 to 

 100 fathoms, and even exceeding that thickness. 



The principal kinds of the pure gypsum found in this forma- 

 tion are the fine granular and compact; the latter, however, is 

 comparatively rare, occurring only in thin layers. But number- 

 less varieties proceed from both by their more or less intimate 

 mixture with swinestone, and, more rarely, with other substances. 

 With these kinds are found also compact and fine granular 

 anhydrite, sometimes of considerable thickness ; specular gyp- 

 sum, in masses 20 or 30 feet long; radiated, in small balls; 

 fibrous, in strings or thin layers ; and earthy, in large nests and 

 pure layers. 



Of the varieties of aphrite found in this formation, the foliated 

 appears in a great measure confined to the purer crystalline 

 portions of gypsum. 



No organic remains have been observed in this formation. 



Caverns are very characteristic of the lower gypsum. They 



