1821.] Mr. Weaver on Ffoelz Formations. 357 



boulders of quartz, hornstone, lydianstone, granite, syenite, 

 greenstone, and quartzy sandstone. The sand is either a pure 

 loose running sand, or it is mixed with clay or marl, and loosely 

 coherent; but both occasionally contain angular fragments of 

 felspar, beside pebbles and grains of quartz, hornstone, granite, 

 syenite, and slaty red sandstone. In the sand, a large well- 

 preserved chamite has been found at the depth of 12 fathoms 

 from the surface, beside fragments of shells. And petrified wood 

 with pieces of bituminous and pyritous wood have occurred in 

 loamy sand, somewhat indurated, at the depth of 40' fathoms. 



Ironstone.-*- This appears in Mansfeld in the form of pure iron- 

 stone, or as ferruginous sandstone. The former is a brown 

 argillaceous ironstone, partly also very siliceous, and either com- 

 pact or ochraceous, and free from petrifactions ; forming layers 

 from half an inch to several inches in tlfickness, or round masses 

 and gaeodes, imbedded in the clay or argillaceous sandstone. 

 The ferruginous sandstone constitutes yellow and brown layers, 

 which are frequently very siliceous, and usually three or four 

 inches thick, and sufficiently rich to be worth smelting. But in 

 Sangerhausen, a bed occurs from two to six feet thick. 



Upper Gypsuni. — This was formerly considered as a distinct 

 formation, the position of which was conceived to be between 

 the new red sandstone and the shell limestone. Later writers 

 have shown its geological connection with clay; and M. Heim 

 views it in the forest of Thuringia as subordinate to the bed of 

 clay, which there intervenes, on either side, between the new 

 red sandstone and the lower and upper limestone formations. 



But in Mansfeld and the adjacent districts, the upper gypsum 

 has no such determinate position, being there found subordinate 

 to the clay and sandstone formation, principally in the clay, but 

 sometimes also in the sandstone, yet in no certain order. The 

 former may be called clay gypsum, and the latter sand gypsum. 



The upper gypsum is found in thick strata horizontally dis- 

 posed, or variously inclined, according to the change of position 

 it may have undergone, being not unfrequently traversed by 

 irregular fissures, often several feet in width, which are either 

 open, or filled with clay, sand, or gravel. The cause of the fre- 

 quently disturbed position of the upper gypsum, and of the 

 concavities by which the surface is marked, is easily to be found 

 in the sinkings of the earth, produced by the rupture and depres- 

 sion of the cavernous formations below. 



In Mansfeld and the adjoining districts, the clay gypsum 

 occurs in the form of large, detached, cliff-like masses, enveloped 

 in the red clay, sometimes constituting a chain of small hills, 

 but never, as in Thuringia, regularly continuous beds. Its posi- 

 tion is indeterminate ; appearing in some quarters in the upper- 

 most beds of clay, almost immediately under the shell lime- 

 stone ; in others, occupying an intermediate position, being 

 covered by an alternating series of beds of sandstone, roestone, 



