114 BASALTIC AND VOLCANIC ROCKS. 



Feet. 



f Chalk . . . . .700 

 I Green Sand .... 500 

 I iron i>and .... 950 

 iSupermedial ) Upper Oolite .... 770 

 Order. ^ Middle Oolite .... 880 

 1 Lower Oolite . . . 820 

 I i\ew Ked Sandstone . . 2100 

 \, 7720 



f Millstone Grit .... 700 

 M ^- J n 1 Coal Measures .... 1000 

 jueaiai ur- ^ (jarbonilerous Limestone . . 850 



I Do. Sandstone and Graywacke 10,000 



12,550 



o L 71 /' Transition Limestone . . 1800 



Suhmedial ' ^^^^^ 2500 



Order. 43qq 



Total 24,350 



CHAPTER XI. 



BASALTIC AND VOLCANIC ROCKS. 



Volcanic Formations. — Trap Rocks,— Mineral Composition.— 

 Augite Kocks. — Basalt. — Gieenstone. — Trachyte.— Clink- 

 stone. — Porphyry. — Amygdaloid. — Lava. — 8c<)rise. — Pumice. 

 — Tuff. — (Conglomerates. — Wacke. — Whinstone. — Pitch- 

 stone. — Volcano (»f Kirauea. — Trap Dikes. — Fingal's Cave. — 

 Slaffa. — Rocks aliered by Dikes.— Faults. — How they cause 

 a Dislocation of^Strata. 



Volcanic formations constitute some of the most ' 

 interesting portions of the globe for the geologist 

 to contemplate ; for here he sees the effects of those 

 causes siill in operation, which, doubtless, have had 

 a powerful influence in consohdating, as well as 

 forming, the earth's surface in the most remote 

 geological epochs. 



The rocks which are recognised as belonging to 

 the present class have been called trap rocks^ from 



