56 THE TRAP FORMATION OF 



shell, or to where the whole mass is nothing but a soft easily workable 

 clay, shewing however still the curved lamellar structure, and what it once 

 must have been. 



No. 8 has an aspect much resembling basalt properly so called, but 

 its fracture is flat and sluggish. 



A cellular, or honey-comb mass, will often occur intermixed with any 

 of the foregoing, — the cells of which are externally empty, and internally 

 filled with powdery whitish oxide of iron, which immediately falls out 

 when the stone is fractured, such is No. 9. 



No. 10 is wacken, with much olivine interspersed. 



And No. 11 has something of green earth, and something of olivine in 

 specks and splashes. 



No. 12 has rather more of a blueish grey than a black caste, probably 

 from the felspar rather exceeding its usual proportions. 



It is much to be wished that the term basalt could be extended so as 

 to include all those rocks named wackens for although there is some 

 slight diversity of fracture and frangibility, and some little variation in 

 colour, yet a difference in name seems quite uncalled for in regard to them 

 and only calculated to mislead. — ^However thus much may be said, that 

 those rocks in this list named basalt, are strictly compact, — ^no casual 

 mineral will be found imbedded, — ^whereas the wackens on the other hand, 

 whilst they are sufficiently compact to exclude any other term than com- 

 pact, are seldom quite entirely so. An accidental mineral of the kinds 

 incident to amygdaloids, may almost always be detected in them, and this 



too. 



