92 T. 8. Hunt on Lithology. 
7 
: 
This disturbance has been traced to the Laurentide hills on the 
Lac des Chats, 140 miles west of Montreal; but to the eastward 
=~ strata exhibit no evidence of this transverse undulation, unless 
Tad to iudicn of the intrusive rocks already mentioned be su 
to indicate the prolongation of a fracture without sensible 
Gislocstion. 
he whole of these eruptive rocks rise through unaltered pa- 
leozoic strata, which, however, in the immediate vicinity of the 
intrusive rocks, exhibit a local metamorphism. The hills of 
Shefford, Brome, and Yamaska break through the strata of the 
Quebec group, and lie a little to the east of the great line of dis- 
location which, in this region, brings up the lower members of 
the paleozoic series against the superior portion of the Lower 
ee and divides into two districts the great paleozoic basin, 
gy of Canada, pp. 234, 597). The other hills all belong 
to “ry ier division of this basin, and break through various 
members of the Lower Silurian series from the Potsdam to the 
— River formation. mong the numerous dikes which 
island; these are of uncertain age, but repose unconformably 
on the Lower Silurian series, and enclose pebbles and masses 0 
Upper Silurian limestone characterized by fossils of the Lower 
eriytioets period. (/bid., p. 356.) 
This g roup of intrusive rocks offers rs very great varieties in 
composition ; thus Shefford and Brome consist of what we shall 
describe as a granitoid eps while the succeeding mountain, 
and from each otter; while Tesi Woukatvite and Mount 
Royal consist in great part of dolerites, presenting however many 
varieties in composition, and sometimes passing into pyroxenite. 
The dolerites of Rougemont and Mount Royal are cut by dikes 
of trachyte. Similar sone also traverse the diorite of bs 
tion of this mountain. nies is probable, judging frous som 
mens from Rougemont, that the dolerite is there vtheroiene al * 
veins of diorite, some of which resemble that of Belceil, a 
others that of Monnoir. Dikes both of trachyte, phonolite, and 
_ dolerite are also found traversing the Lower Silurian strata 1m 
the ‘gahet of the great eruptive masses ; “a the conglomerate 
‘len’s mentioned above is traversed by dikes of dol erite, 
