FLCETZ TRAP FORMATIONS. 2(1 



which sometimes exhil)it a prismatic form. It fliUs readily 

 into large angular fragments, hut srems strongly to resist 

 that progress of disintegration which il must undergo heforc 

 it can be removed by the water. The face of the perpendi- 

 cular piecipices which it forms is often marked by large 

 parallel vertical seaiiis. Following the water courses, which 

 are sunk a considerable distance l)flu\v ilie smface. the line 

 of separation from the" sandstone on which the greenstone 

 rests at length becomes visil)Ie. The saiidrock in these places 

 has its strata nearly or quite horizontal, and in all other cha- 

 racters is similar to what we have formerly mentioned. 



2. Amygdaloid. Kirxcan. ManJelstein, IVerner. Roche 

 amygdaliiide. nrochnttt. 



\\c ajjply tliis name to a porous or vesicular rock of a very 

 daik grey, greenish, or l)lack colour, usually accompanying 

 the greenstone, and sometimes in connection with the sand- 

 stone. In its ultimate composition it resembles greenstone, 

 but I have never seen in it such large fragments of feldspar 

 and scales of mica as are observed in that rock. The cavi- 

 ties which occur in every part of the substance of this rock 

 are of various sizes, some of them havina; the appearance of 

 bubl)les which had been formed in a semifluid mass and af- 

 terwards lengthened and variously distorted by the motions 

 of the contiguous matter. Near the surface they contain a 

 soft while or yellowish cari)onate of lime nearly fdling tlic 

 cavity and giving to the recent surface a variegated or spot- 

 ted appearance. In surfaces which have for some time been 

 exposed to the air. this soft substance has been removed, 

 and tlie little cavities are found empty. 



Amygdaloid does not appear to occupy any great extent 

 of the country near the Hoeky Mountains. I ha\e not met 

 with it imbedded in, or surmounted by. any other rock. It 

 forms conic hills like the greenstone liefore mentioned, and 

 these sometimes occur ir) deep waterworn valleys l)outi(led 

 on l)oth sides by precipices of fjandrock rising much above 

 the elevation of the amvgdaloid. It is likewise seen In the 

 high plains, sometimes in narrow and crooked ridges, as if 



