Minerals in Graywacke. 



283 



" In an economical light," says Dr. Macculloch, " it must be fruitless 

 to search for coal be] ow the old red sandstone, and, generally speak- 

 ing, beneath the mountain limestone ; as to mine after primary coal 

 (anthracite as I understand him,) would be a wild project."* " Anthra- 

 cite," says Beudant, " on account of the difficulty with which it is 

 kindled, cannot be employed but in furnaces with a good draught."! 

 " The difficulty which is experienced in the combustion of anthracite," 

 says Dumas, " is a very great obstacle to every economical use of that 

 body. — It is possible, indeed, that anthracite will one day become use- 

 ful in deep furnaces ; although in almost every other process of the 

 useful arts, its employment can be hardly practicable, on account of 

 the high temperature which it requires to complete its combustion. "J 



The other minerals that have been found in the graywake of Mas- 

 sachusetts and Rhode Island, are few and unimportant. It is hardly 

 necessary to mention such common and widely disseminated minerals 

 as iron pyrites, crystalline quartz, and calcareous spar. Magnetic 

 iron ore and the micaceous oxide, have also been found in this group 

 in small quantities : and I have already mentioned crystallized epi- 

 dote, in the varioloid wacke. In the amphibolic aggregate, in New- 

 port, I found a vein of crystallized zoisite, about four inches wide, and 

 several feet long. In other parts of the globe graywacke is a repos- 

 itory of gold ; and the clay slate connected with it, (transition clay 

 slate,) contains the richest veins of silver in New Spain, according to 

 Baron Humboldt. || But neither of these metals have been found in 

 these rocks in Massachusetts. 



In the varioloid rocks of Brighton, Professor Webster has found sul- 

 phate of lime and baryta. The latter is said to occur also in Milton: and 

 also fibrous limestone in thin veins in wacke. Adularia andsulphu- 

 ret of copper have been found also at Brighton. Efflorescent and mas- 

 sive sulphate of iron has been found, according to the Messrs. Da- 

 nas, on the argillaceous slate in Charlestown. 



Dr. Robinson says that the graywacke, near Providence, is tra- 

 versed by veins of quartz, containing fluor spar. 



In Brighton, in the varioloid wacke, I noticed fibres of green asbes- 



* System of Geology, vol. 2. p. 305. London 1831. 



t Traite De Mineralogie, vol. 1. p. 717. Paris 1830. 



t Traite de Chimie Appliquee aux Arts, vol. 1. p. 606. Paris, 1828. 



II Superposition of Rocks, p. 105. 



