354 r. w. ells — laurentian of the ottowa district. 



Recent Investigations necessitate Change in the Section-. 



Within the last forty years the settlement and opening up of this 

 country has gone forward at a comparatively rapid rate. Great areas 

 have been cleared, and roads penetrate the townships in all directions 

 and extend northward along the principal rivers for over one hundred 

 miles, so that cross-sections are readily afforded and areas easily studied, 

 concerning which thirty or forty years ago the information was merely 

 conjectural; from the work of late years, therefore, it has heen found 

 necessary to make very important changes in the section, as just stated. 



The Anorthosite Masses north of Saint Jerome. 



In the eastern portion the study of the anorthosite masses north of 

 Saint Jerome by Dr F. D. Adams has conclusively shown that these are 

 of intrusive origin, since in many places they cut directly across the 

 strike of both the gneiss and limestone, while in others they have come 

 to the surface in long dike-like bands along the lines of sedimentation of 

 the gneiss. With the anorthosite proper are sometimes associated, more 

 particularly along the lines of contact with the gneiss, zones of gabbro 

 rock, while pegmatization is frequently seen in the former as we approach 

 the junction. 



Trembling Mountain Section Re-examined. 



A careful reexamination of the Trembling Mountain section westward 

 to the Iroquois chute on the Rouge river, and which was formerly re- 

 garded as an ascending one, shows that this view cannot be maintained. 

 In this space no less than three anticlinals with their corresponding 

 synclinals occur, while the section is further complicated b}^ faults of 

 very considerable extent. Of the hands of limestone said to occur there, 

 only one. namely, that of Trembling lake, was found, and this hand, 

 instead of occurring as an interstratified portion of the orthoclase-gneiss 

 scries, presents the form of a synclinal with converging dips in the un- 

 derlying gneiss both on the east and west sides of the lake, the western 

 flank of the Trembling mountain, which comes down to the east shore 

 of the lake, having a regular dip to the northwest of 60°, upon which the 

 limestone is seen to rest and to form part of ;i small island in the lake, 

 while on the west side of the lake great hills of gneiss, similar to that of 

 Trembling mountain, occur mid show a southeast dip toward the water 

 of from 40° to ( .M)°. The Limestone itself, which from its position forms 

 the lowest calcareous member given in the original section, shows first 

 at the discharge of the lake from the south end in a band exposed for 



