

392' '•' Mineralo^ical Notices. 



Another diabase contains crystallized prehnite in prisms. It» 

 hornblende afforded a different composition from the above3 as 

 follows : 



Si ^1 te SEa Ca Mg fl 



Hornhlend^, 50-9 49 21-2 irace 11-2 S'T 1"6, alkalies and loss I'o 



The feldspar of the rock is andesite as before, giving : 



Si S:l Pe Ca Ifig ]?fa K fi: 



Andesite, 69-9 25-1 ^race 3-7 O'T 7'4 1'2 1'7 = 99-7 



A schistoid diorite is a common rock in L'Oisans, There is 

 also a granitoid diorite^ consisting largely of whitish feldspar with 

 disseminated hornblende crystals of a deep black color. The 

 feldspar is andesite. This same feldspar is also found in the 

 euphotide of Lavaldens in the department of L'Isere. This rock 

 consists of deep olive green lamellar diallage and the white ande- 

 site ; the latter afforded on analysis 



Si *1 3Pe Ca Slg alkalies (diff.) fl 



60 2a-8 - H 6-0 1-5 5'3 2-3=100 



[A doubt existed among some members of the Geological So- ^ 



ciety with regafd to the feldspar in the above analyses being ande- 

 site, on the ground that the rocks in which it has been reported 

 to be found may contain some free silica; but this Delesse denies.] 



Lava, — Rammelsberg makes the lava of Thjorsa, Iceland, 

 from the analysis by Genth (given in this Journal, vol. viij 2nd 

 series, p. 114,) to consist of anorthite 55-59, augite 40*46; olivine 

 4-51. The Thiorsauite of Genth is impure anorthite according 

 to this chemist. 



For the lava of Hals, Iceland, which has a grayish black color 

 and sp. gr. 2-919, he gives the composition, lime-oligoclase 63, 

 augite 2S, olivine 9. That of Efrahvolshraun, which is uncrys- 

 talline, with a black color inclining to gray and sp. gr. 2*776, 

 consists, according to him, of 71-37 of linie oligoclase and 29'66 

 augite (including olivine and magnetic iron). 



The lava of Etna was determined by Abich some years since, 

 to be composed of 54-80 labradorite, 3446 augite, 7-98 olivine, 

 and 306 magnetic iron = 100. That of Stromboli, according to 

 the same author, consists of 48-18 labradorite, 44*91 angite, 6*91 

 magnetic iron, or 44-30 labradorite, 39*12 augite, and 16*58 oli- 

 vine. That of Vesuvius, of 60-19 leucite, 20-44 augite, 10*42 

 olivine, 8-95 magnetic iron =100. ' 



Rammelsberg also observes that the Juvenas meteoric stone 

 has the same coniposition as the Thjorsa lava of Hecla, it con- 

 sisting of anorthite and augite in nearly the same proportions- 



Red Antique Porphyry. — Delesse has examined this rock with 

 important results, (Bull. Soc. Geol de France, vii, 524, 1850.) 

 The feldspar is in small oblong macled triclinic crystals, of a 

 whitish or rose color^ rarely greenish. G=2'690. Composition' 



r 



