Se ed 
SP SES ee ee be 
J. D. Dana on the characters distinguishing Kinds of Rocks. 839 
tion, it now makes little of it. Thirdly, it is not sustained by 
the analyses of the varieties of foliated pyroxene—diallage, 
and the wrongly called hypersthene being essentially identical 
in composition with common augite of eruptive rocks, an 
SiO, Al,O, FeO MnO MgO CaO H,0O 
Florence, Diall.... 53-20 2°47 8°67 0°38 14°91 19-09 1-77=100-49, Kohler. 
Piedmont, Diall... 50°05 2°58 11°98 — 99°61, Regnault. 
Harzburg, Hyp. .. 52°34 3°05 8°84 8 0°66= 99°65, Streng. 
84 —— 15°58 19°] 
Neurode, Hyp. _.. 53°60 1:99 8°95 0°28 13-08 21-06 0°86= 99°82, v. Rath. 
Etna, Augite Cryst. 50°55 4:85 7-96 —— 13-01 22°29 —-= 98°66, Kudernatsch. 
esuvi 50°90 5°37 6:25 —— 14:43 22°96 —-= 99-91, Kudernatsch. 
. Vesuvius, “ 49°61 4-42 9°08 —— 14:22 22-83 ——=100°16, Rammelsberg. 
The mineralogical and chemical differences are thus too 
mon serpentine. Ferber in his “ Briefe aus 
dem Walschland” (Letters from Italy), written in the years 
1771, 1772, and published in 1778, describes so_well the rock 
der greasy to the touch (the diallage) and also amianthus. He 
then adds that “in horizontélen Schichten in den Gabbro-Bergen 
aus weissen Feldspat, der an einigen Stellen Kalchspatartig ist 
und mit Siuren brauset, etwas grinlichtem silberfarbigen wiir- 
flichten Glimmer, und griinlicher Serpentin-Erde, besteht :” 
a description that distinguishes the gabbro from the granitone. 
F urther, he says, that some of the granitone consists of the 
‘White feldspar in large parallelopipeds and green gabbro- 
earth, without the micaceous mineral.” - 
