254 J. F NEWSOM CLASTIC DIKES 



coal. The larger dikes are left b}^ the miners, and in a plan of the mine 

 they show a rectangular arrangement, as though the intrusions had been 

 along the joints of enormous rectangular blocks of the coal. The dikes 

 of these coal beds are undoubtedly intrusions. Figures 1 and 2, plate 31, 

 show the nature of some of these intrusions. 



Clastic Dikes previously Described 



The follow^ing references to literature on clastic dikes are arranged in 

 chronological order. In some cases extracts from the papers are given ; 

 in others a few words of explanation and the conclusions are given. A 

 few references to dikes of clay, shale, and sandstone in coal beds are 

 given. Such dikes are common in many coal regions and references to 

 some of those that have been described are inserted in order to bring 

 them to the attention in connection with the subject of clastic dikes. It 

 is also desired to call attention to the similarity between such dikes in 

 coal beds and the clastic intrusions that occur in regions far removed 

 from coal beds. 



A number of references are also given to papers by English and other 

 authors concerning pipe-like deposits of sand, of gravel, and of clay, 

 which are found in the chalk and limestones in a number of regions. 



Inasmuch as asphaltum is more or less closely associated w^ith many 

 sandstone intrusions and is derived from sedimentary rocks, a number 

 of references are given on the subject of asphalt veins : 



Strangways, 1821. The earliest reference to dikes of clastic materials 

 seems to be that of Mr Strangways, who described a number of dikes of 

 clay near the village of Great Pulcovca, in the neighborhood of Saint 

 Petersburg, Russia.* 



The dikes intersect limestones and blue clay, and are described at one 

 place as " about two feet wide, and are filled with diluvian gravel of the 

 same nature as that which covers the plain and cliff above." 



Cuvier and Brongniart, 1822. In 1822 Brongniart and Cuvier called 

 attention to sand pipes in the neighborhood of Paris.f 



Murchison, 1827. In speaking of the rocks of Kintradwell in Somer- 

 setshire, in 1827, Murchison says : X 



" These grits are traversed by a vein two and a half feet wide, in texture resem- 

 bling quartz-rock and having a conchoidal fracture; the tilting of the strata in 

 opposite directions at this point indicates some powerful disturbing cause." 



That Murchison referred to a dike of hard sandstone instead of to a 



♦Trans. Geol. Soc. of London, vol. v, 1821, pp. 386, 407, 408, pis. 25, 26, 27, 28. 

 t Description g6ognostiques des Environs de Paris, edit. 1822, pp. 76, 134, 141. 

 I Trans. Geol. Soc. of London, 2d series, vol. ii, p. 304. 



