T. S. Hunt on Lithology. * 99 
earthy carbonates, and closely resembles in its aspect certain tra- 
chytes from the Siebengebirge on the Rhine. Other varieties 
can scarcely be distinguished from the so-called domite, the tra- 
chyte of the Puy de Déme, and exhibit small drusy cavities, 
cate, which in the trachytes of Brome appears only as rare crys- 
tals of nepheline, and in Chambly as analcime and chabazite. In 
Some of the compact and earthy varieties about Montreal, how- 
ever, this soluble silicate exists to a large extent, and has the 
Composition of natrolite. By this admixture of a zeolite the 
wachytes pass into phonglite. 
The first of these trachytes which will be noticed forms a dike 
hear McGill College. The rock is divided by joints into irregu- 
lar fragments, whose surfaces are often coated with thin bladed 
crystals of an aluminous mineral, apparently zeolitic. I 
brilliant crystals of cubic iron-pyrites, often highly modified, are 
* 
isseminated through the mass, The rock has the hardness of - 
feldspar, and a specific gravity of from 2°617 to 2°632. Its color 
18 white, passing into bluish and grayish-white; it has a feebly 
shining lustre, and is slightly translucent on the edges, with a 
Compact or finely granular texture, and an uneven sub-conchoidal 
ture. Before the blowpipe it fuses with intumescence into 
4 white enamel. The rock in powder is attacked even by acetic 
acid, which removes 0°8 per cent of carbonate of lime, besides 
15 per cent of alumina and oxyd of iron; the latter apparently 
derived from a carbonate. Nitric acid dissolves a little more 
lime, oxydizes the pyrites, and takes up, beside alumina and al- 
kalies, a considerable portion of manganese. This apparently 
©xists in the form of sulphuret, since, while it is soluble in dilute 
hitrie acid, the white portions of the rock afford no trace of 
Manganese before the blowpipe; although minute dark colored 
hs, associated with the pyrites, were found to give an intense 
