NATURE OF THE ROCKS. 341 



changes, but, probably, the unequal solidity of the 

 stone composing the masses of rock which are 

 piled one over the other. In places where I had 

 opportunities of observing these formations, I saw, 

 analagous to the change of the clayey, flinty, and 

 sandy places, in one and the same layer, masses of 

 crumbly clay, slate, loose sandstone, and conglo- 

 merate, firm porphyry and amygdaloid, alternate 

 with each other ; and of the two last, grotesque 

 rocks, and rugged walls, produced by the washing 

 away and sinking together of their softer interve- 

 nient layers, rising among dreary ruins. 



Not less interesting than the kinds of rocks just 

 mentioned is the appearance of the porphyry-slate 

 and rocks resembling basalt, at Oonalashka. Do 

 they belong here to the formation of the older 

 floetz sandstone, or to the floetz trap ? These 

 questions, which force themselves upon us, cannot 

 indeed be satisfactorily answered for want of know- 

 ledge of the stratification of the two kinds of rock, 

 but the supposition may be hazarded, that these 

 rocks belong to the floetz trap. Indissolubility, 

 greater hardness, by which the piece No. 30. 

 is distinguished from real basalt, seem to be 

 owing to quartz and augite, which here form a 

 chief ingredient of the rock, though otherwise 

 only sprinkled, like porphyry, in basalt. But that 

 this stone contains augite, speaks for the affinity 

 with the real floetz trap, which is farther confirmed 



z 3 



