328 A. E. BARLOW — LAURENTIAN AND HURONIAN ROCKS. 



any sharp line of division between the two rocks would suggesl the 

 probability that both belonged to the same period of irruption, the more 

 rapidly cooling diabase being intruded by the more slowly cooling 

 granite mass. The diabase (according to .Air Ferrier) shows evidence 

 under the microscope of having been subjected to great pressure, doubt- 

 less produced before the cooling of the granite magma, while the granite 

 is comparatively free from any such evidence. The gneiss and granite 

 contain numerous sharply outlined fragments of a dark-gray schistose 

 rock which Pumpelly and Van Hise stated I classed as Huronian, 

 whereas, in their opinion, these' were pre-Huronian. From their article 

 one would infer that there existed at this locality a. large mass of these 

 schists from which the smaller fragments had become detached, but 

 beyond a mass of diabase such as described above and of which they 

 make no mention, there seems to be no rock-mass from which these 

 fragments could have been derived. These schists, however, do not in 

 the least resemble the micaceous schists and quartzites described by me 

 in contact with the Laurentian through the Sudbury district, for the 

 former shows no trace whatever of clastic structure, while the fragmental 

 origin of the Sudbury schists may readily be seen in the field or in a 

 thin slice under the microscope. The banded appearance of the Thes- 

 salon schists points to a possibility of an original fragmental condition, 

 but such must remain merely hypothetical, on account of their extreme 

 alteration. The late Mr Alexander Murray, on his manuscript map of 

 this district, frequently alludes to this granitic mass as " red and green 

 trap " or (i syenite." and both he and Sir William Logan * were of opinion 

 that the granite was later than tin 1 Huronian strata with which it comes 

 in contact. 



The Huronian is represented by what Pumpelly and Van Hise char- 

 acterize as a "great basal conglomerate," the detritus from which it was 

 formed resulting from the disintegration of the gneiss and granite. As 

 close an examination as possible was made of the line of junction, but 

 the length of contact exposed is far too small to come to any undeniable 

 conclusion. The very frequent angular or subangular outline of the in- 

 cluded fragments in this rock point out the probability that the so-called 

 conglomerate is in reality a volcanic agglomerate or breccia, whose frag- 

 ments, thrown down in water, have become more or less rounded and 

 mixed with finer arenaceous material. Besides, the conditions of con- 

 tact on the two islands are essentially different. On one island the 

 junction is so sharp and distinct that the line of division can be placed 

 to the fraction of an inch. However, its abrupt change in strike ("at 



*Geol. Canada, 1863, p. 58. 



