766 The American Naturalist. [September, 
MINERALOGY AND PETROGRAPHY:.' 
Mt. Hekla Liparites.—The material of three new liparite streams 
from the vicinity of Mount Hekla, in Iceland, and that of the one 
described by Preyer and Zirkel’, have been examined by Backström.’ 
In all the rock consists of phenocrysts of orthoclase and green pyrox- 
ene in a more or less glassy hyalopilitic groundmass without peculiar 
features. One specimen contained small grains of olivine and another 
accumulations of tridymite. None of the streams originated at Hekla. 
Their source is not known. A granophyre from the north coast of the 
Snaffel Peninsula is mentioned by the same author as containing plag- 
ioclase grains, surrounded by orthoclase zones, and these in turn by 
micropegmatitic intergrowths in which the orthoclase is orientated 
with the same mineral in the zone around the plagioclase. This and 
other granophyric liparites in the neighborhood are very similar to 
the ‘ Krablite’ inclusions thrown out from the crater of Viti. Of the 
other liparites of different ages described by the author some are 
trachytic in character and others are granophyric. In discussing 
their general features Backström separates them into true liparites, 
liparite glasses and granophyres, composed essentially of feldspars, 
pyroxene, iron oxides, zircon and glass, to which are sometimes added 
quartz, tridymite, apatite, olivine and occasionally hornblende, biotite, 
hypersthene and sphene. The rarity of biotite is notable. Of the 
feldspars plagioclase was found in every specimen examined and sani- 
dine in but few. Nevertheless the percentage of CaO in the rocks is 
small. Upon comparison of seventeen analyses of fresh specimens of 
the Icelandic liparites it is found that the amount of sodium in them 
exceeds that of potassium, and that in this respect the Iceland district 
differs materially from that of the Great Basin and of Hungary. 
Bostonite and Monchiquite from Lake Champlain.—A 
recent abstract of a paper on the trap dykes of the Lake Champlain 
Valley by Messrs. Kemp and Marsters* is very interesting, as it makes 
known the existence there of two rare types of dyke rocks, bostonite 
‘Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 
*Reise nach Island. Leipzig, 1862, p- 346. 
*Geol. Foren. Forh., xiii, 7, p. 639. 
‘Trans. N. Y. Acad. Sci., xi, 1891. 
