556 



VOLCANIC ROCKS OF THE 



[Ch. XXXIL 



one or two tons in weight, intermingled with pebbles of -other rockS: 

 These angular fragments were probably thrown out from volcanic vents, 

 and fell upon sedimentary matter then in the course of deposition.* 



Carboniferous period. — Two classes of contemporaneous trap rocks 

 have been ascertained by Dr. Fleming to occur in the coal-field of the 

 Forth in Scotland. The newest of these, connected with the higher series 

 of coal-measures, is well exhibited along the shores of the Forth, in Fife- 

 ^hire, where they consist of basalt with olivine, amygdaloid, greenstone, 



Tig. 679. 



Eock and Spindle, St. Andrew's, as seen in 1838. 

 a. Unstratified tufif. h. Coluninar greenstone. c. Stratified tuffi 



* De la Beche, Geol. Proceedings, Xo. 41, p. 198. 



