1821.1 Mr. Weaver on Floetz Formations. 407 



fragments of shells, the substance of which is mostly yellowish- 

 grey and foliated, cemented by an ochre-yellow sandy medium. 



The yellow varieties are usually more clayey, or sandy and 

 tender, than the grey homogenous kinds ; but some of them are 

 partly 'of a magnesian quality, locally known by the name of 

 mehlbatz. They all, however, distinctly alternate with each 

 other, in beds of greater or less thickness. 



Sometimes the dark-grey compact argillaceous limestone con- 

 tains fragments of compact limestone, of various sizes, then 

 acquiring a spotted appearance. 



The compact shell limestone of the Seeberg, near Gotha, is 

 partly oolitic ; small compact round and oval grains, of a dark- 

 grey colour, being immersed in a yellowish-grey base, and form- 

 ing a stratum two feet thick.* 



Cylindrical channels, from one-fourth to halt an inch in 

 diameter, several inches in length, and closed at both extremi- 

 ties are very common in the shell limestone, particularly in that 

 -which is pure and compact. These channels are straight, or 

 thev wind in various directions, the sides being smooth ; and 

 solid cylinders of a similar form, separating easily with a smooth 

 surface, are also common. Their origin is unknown. 



In most districts, one or more layers of flint, hornstone, or a 

 compound of the two, may be met with in the shell limestone ; 

 but they rarely exceed a few inches in thickness, and are seldom 

 continuous for any great distance. Sometimes also these sub- 

 stances appear in the form of nodules.f And in Henneberg are 

 found in the shell limestone several layers of yellow and brown 

 siliceous limestone, which in some parts pass into distinct yellow 

 and brownjasper, and in others into siliceous brown ironstone. 



White calcareous spar, in rather large masses and druses, and 

 in disseminated grains, appears also sometimes in the shell lime- 

 stone ; and stalactiform and botriform calcsinter is found inci- 

 dentally between the strata. 



Slaty and earthy aphrite have occurred in it near Polleben, m 

 Mansfeld, and agaric mineral near Asse, in Wolfenbiittel. 



Compact and fibrous gypsum, in layers extending nearly to 

 two feet in thickness, have been found, it is said, in the shell 

 limestone, near Naumburg.j: Potter's clay occurs in it near 

 Freyburg, on the Unstrutt. 



Organic Remains. — The pure and marly beds of the shell 

 limestone appear to contain a greater quantity of petrifactions 

 than those which are sandy. The remains of bivalve and uni- 

 valve shells are numberless ; sometimes forming a congeries of 

 shells in layers from a half to one inch thick between the strata; 

 while others occur in the substance of the limestone. 



* The oolitic structure appears in a lew instances also in the English lias limestone, 

 ■f These substances occur under the same forms in the English lias limestone. 

 X Gypsum is met with also in the shell limestone formation of England, In groups 

 Ho. 12, 10, and 9, of Mr. Greenough's Geological Map. 



