RE-EXAMINATION OF TREMBLING MOUNTAIN SECTION. 355 



about fifty feet, It appears also in several small islands near the center 

 and northern half of the lake, where it has at one place a breadth of 

 about 75 feet. In its northern part this hand changes its course from a 

 nearly north direction to one nearly at right angles to it, and appears to 

 be abruptly terminated against the bold walls of gneiss which extend 

 along the west shore of the lake. The remaining part of the section 

 crossing Great Beaver, Long and (liven lakes shows no limestone in any 

 portion, with the exception of a small outcrop from two to three feet in 

 thickness, of impure character, associated with gray and rnsty gneiss on 

 a small island near the north end of Long lake. The timber along the 

 shores of this lake being recently burnt off, a succession of ledges of red- 

 gray gneiss of the usual aspect is disclosed, which here have a general 

 dip to the west, the reverse dip to the east being clearly seen in the gneiss 

 ridges which extend for some distance along the east side of the Rouge 

 river below the Iroquois chute. It is but just to say that in the com- 

 pilation of this section the notes of survey and of the geology as well 

 were furnished by one of Sir William Logan's assistants, whose techni- 

 cal knowledge was limited and employed in making a topographic 

 sketch of the area in question. 



The thickness of the Trembling Lake band of limestone is difficult to 

 estimate, but it is not apparently great, since, from the portions exposed, 

 at no point is there more than fifty feet in vertical thickness seen. The 

 area beneath the water is uncertain, and any attempt to estimate it in 

 such a folded series of strata would be only conjectural. 



Region between Anortiiosite Area and Gatineau River. 



In the region embraced between the Anortiiosite area north of Saint 

 Jerome on the east and the river Gatineau on the west, a distance of 

 about eighty miles, several traverses have been made both by canoe 

 along the lakes and rivers and by measurements along the roads which 

 have been opened up in the country north of the Ottawa, and thus a 

 very good opportunity has been presented of studying the structure in 

 detail over a very considerable area, It will be observed that in all the 

 reports, both of Logan and Murray, on the Laurentian the folded and 

 sometimes overturned character of the strata is pointed out. The great 

 resemblance in the character of the gneiss at the various horizons, sup- 

 posed to be separated by the different limestone bands, and the great 

 similarity in the bands of the limestone as well, is also frequently noted. 

 A close examination of the limestone outcrop throughout the whole 

 eighty miles of the section indicated has led us to the conclusion that 

 in nearly every case the limestone bands occupy well-defined synclinals, 

 which are separated by anticlinals in the underlying gneiss ; that in 



