chap. iv. Basaltic Series, 85 



flowed over and concealed portions of it. In some 

 parts, where the basaltic ring had been breached, and 

 the black ramparts stand detached, the feldspathic 

 lavas have passed between them, and now overhang 

 the sea-coast in lofty cliffs. The basaltic rocks are of a 

 black colour and thinly stratified ; they are generally 

 highly vesicular, but occasionally compact ; some ol 

 them contain numerous crystals of glassy feldspar and 

 octahedrons of titaniferous iron ; others abound with 

 crystals of augite and grains of olivine. The vesicles 

 are frequently lined with minute crystals (of chabasie ?) 

 and even become amygdaloidal with them. The 

 streams are separated from each other by cindery 

 matter, or by a bright red, friable, saliferous tuff, which 

 is marked by successive lines like those of aqueous 

 deposition ; and sometimes it has an obscure, concre- 

 tionary structure. The rocks of this basaltic series 

 occur nowhere except near the coast. In most volcanic 

 districts the trachytic lavas are of anterior origin to the 

 basa 1f ic ; but here we see, that a great pile of rock, 

 closely related in composition to the trachytic family, 

 has been erupted subsequently to the basaltic strata : 

 the number, however, of dikes, abounding with large 

 crystals of augite, with which the feldspathic lavas have 

 been injected, shows perhaps, some tendency to a re- 

 turn to the more usual order of superposition. 



Basal submarine lavas. — The lavas of this basal 

 series lie immediately beneath both the basaltic and 

 feldspathic rocks. According to Mr. Seale, 1 they may 

 be seen at intervals on the sea- beach round the entire 

 island. In the sections which I examined, their nature 

 varied much ; some of the strata abound with crystals of 



1 ' Geognosy of the Island of St. Helena ' Mr. Seale has con- 

 structed a gigantic model of St. Helena, well worth visiting, which 

 is now deposited at Addiscombe College, in Surrey. 



