Vol. 52.] BASALT-PLATEAUX OF NORTH-WESTERN EUROPE. 347 



to which I have referred as occasionally displayed by the plateau- 

 basalts. More than 60 feet of agglomerate is visible in vertical 

 height from where its base is concealed by debris and vegetation to 

 where its upper surface passes under a banded rock to be afterwards 

 described. That this unstratified mass of volcanic ejectamenta marks 

 the site of the vent can hardly be doubted, although denudation 

 has not revealed the actual walls of the chimney. The steep 

 grassy slopes do not permit of the relations of the rocks being every- 

 where seen, but the agglomerate appears to pass laterally into 

 finer, rudely stratified material of a similar kind, which extends 

 east and west of the vent as a thick deposit between the bedded 



Fig. 11. — Section of volcanic vent and connected lavas and tuffs. 

 Scorr, Camas Garbh, Portree Bay, SJcye. 



,cr 



MiMP 



>\-< 



wflaa^^^i^^iiij 



UZfTf 



»I 



a. Rudely-bedded dull green tuff ; b. Coarse agglomerate ; c. Prismatic basalt ; 

 d. Massive jointed basalt ; e. Red banded decomposing rock, probably of 

 detrital origin;/. Plateau-basalts, prismatic and rudely columnar ; g. Dyke 

 of dolerite, somewbat vesicular, 5 to 6 feet broad ; h. Basalt dyke 2 to 3 feet 

 broad ; i. Dyke or sill of basalt similar to h, and possibly connected 

 with it. 



basalts. Possibly denudation has only advanced far enough to lay 

 bare the crater and its surrounding sheets of fragmentary material, 

 while the chimney lies still buried underneath. 



East of the agglomerate the fragmentary material becomes less 

 coarse, and shows increasing indications of a bedded arrange- 

 ment. Close to the agglomerate the dip of the coarse tuff is 

 towards that rock at about 10°. A few yards farther east a 

 sheet of very slaggy basalt is seen to lie against the tuff, which it 

 does not pierce. The vesicles in this adhering cake of lava have 

 been pulled out in the direction of the slope till they have be- 

 come narrow tubes 4 or 5 inches long and parallel to each other. 

 Some parts of this rock have a curved ropy surface, like that of 

 well-known Yesuvian lavas, suggestive of the molten rock having 

 flowed in successive thin viscous sheets down the slope, which has 

 a declivity of about 30°. This part of the section may possibly 

 preserve a fragment of the actual inner slope of the crater, formed 

 of rudely bedded tuffs. 



