562 THE WONDERS OF GEOLOGY. Lect. V. 



to that of a large cannon-ball ; and these are often grouped 

 together like bunches of grapes, or masses of chain-shot. 

 On the coast of Durham, the whole cliff is made up of 

 large concretional clusters, resembling piles of cannon- 

 balls. This phenomenon is best seen near Sunderland, 

 and along the shore near Marsden and Black rocks ; where 

 it is associated with other curious and interesting modifica- 

 tions of concretional action.* These masses offer a beautiful 

 illustration of spheroidal structure, superinduced on strati- 

 fied detritus after its deposition; for the sedimentary 

 laminae pass through the globular concretions uninterrupt- 

 edly. The limestone is commonly traversed by veins and 

 strings of carbonate of lime, and occasionally contains 

 hollow spheroids of calcareous spar, and crystals of sul- 

 phate of strontian and barytes. Galena, or sulphuret of 

 lead, sulphuret of zinc, calamine, and carbonate of copper, 

 also occur ; and some veins of galena in the Mendip hills 

 have yielded profitable returns.t 



18. Permian of Germany and Russia. — In Thurin- 

 gia, in Saxony, the magnesian limestone (Zechstein) is 

 largely developed, and associated with beds of dark bitu- 

 minous shales and marls highly charged with copper pyrites, 

 which are termed Kupfer-schiefer. These shales have 

 long excited the attention of naturalists, from the number 

 and variety of the fossil fishes they contain, and the 

 peculiar mineralized condition in which these relics occur ; 

 specimens from Eisleben in Mansfeld, a celebrated produc- 



* See an admirable memoir^" On the Geological relation and internal 

 structure of the Magnesian Limestone," by the Rev. Adam Sedgwick, 

 Geol. Trans, vol. ii. p. 50. The dolomitic conglomerates around 

 Bristol are ably described by Dr. Buckland and Mr. Conybeare, Ibid, 

 vol. i. A valuable paper by Messrs. Murchison and Strickland, on the 

 "Upper New Red of Gloucestershire," &c. will be found, Ibid. vol. v. 

 p. 331. 



f Geology of England and Wales, p. 304. 



