304 On the Geology of the Island of Montreal. 



semblance to sienite. This white compound, disintegrating 

 by the weather, falls out, and renders the crust of the rock 

 vesicular. Copper-coloured mica, in single scales, or in 

 nests, is common in this variety, and now and then, though 

 rarely, in great quantity. Small druses often form in the in- 

 terstices of the hornblende crystals, lined with small crystals 

 of feldspar, (white or colourless, transparent, hexahedral, ta- 

 bles) quartz, pale green epidote, (granular or in stellular, ra- 

 diating, acicular crystals) white zeolite, (in divergent, coarse, 

 acicular crystals, terminally superimposed,) and rarely a small 

 weathered rhomb of chabasite. Cubic iron pyrites is common, 

 and spicular iron ore in confused crystallization, as a coating. 

 This form is met with on the summit of the east division of 

 the hill, above McTavish's Tomb, on the middle of its north 

 and west flanks, and the greater part of Mount Trafalgar, es- 

 pecially the lower. On the northeast declivity of Mount Tra- 

 falgar, and on a cleared hummock on the east division, near 

 the west road to St. Catharine, the crystals of hornblende ar- 

 range themselves in continuous lines or bands, from a sixth to 

 half an inch thick, and sometimes several feet long; with oc- 

 casional cross rents. They are parted by the mixture of 

 quartz and feldspar above-mentioned : forming, of course, 

 similar bands, but white. I have seen this curious structure 

 in short spaces only, and am thence unable to state its extent 

 or direction. It is the more remarkable, as occurring among 

 rocks in which any thing like order seems studiously avoided. 

 It would appear to indicate that the mass has consolidated 

 during motion. This kind affects the magnet. 



The second form exists in most parts of the hill, and in the 

 route of the Lachine Canal, and is well marked in the low 

 cliff above McTavish's Tomb. It is black, or brownish black, 

 opaque, homogeneous, rather fine-grained, with blunt edges. 

 It yields a gray streak readily to steel. Its specific gravity is 

 that of trap rocks general!} 7 . The specimens taken from near 

 tfae west road to St. Catharine, and in other places near 



