Sf; Vol. XLiri, Art. r,. _ s T,v.l)oi 



Of the four analysed rocks, two (B and C) belong to auvercjnose 

 (ail. '5. 4. 4^), one (D) to handose (IF. 4^ 4'. 5.), and one (A) to 

 an unnamed subrang ('III. 4. '5. 4.). The average of the four 

 analyses places the rock at 'III. 4'. 4'. 4. 



JSame of Mock. — As is clear from the above description, the 

 rock is basaltic, but is remarkable in its amount of silica relative 

 to other components. This amount is not only sufficient to form 

 the highest silicates but yields it to excess, which appears in the 

 norms as occult quartz, so tliat the rock finds its position in 

 average at the quardofelic order in the C. I. P. W. quantitative 

 system. The normative plagioclase, on the other hand, is as 

 calcic as bytownite (Abi-Ana, in A, Ab^.,An;s in B, Ab.^^An-, in C, 

 A]).^An-y in D, and Ab.. Am, in average). The rock is, therefore, 

 an aphanite belonging to the qucu-dofeUc order or very near to it,, 

 villi the normative hytoirnite. 



The rocks with strongly calcic normative plagioclase usually- 



