BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 4, pp. 349-360 August 7, 1893 



THE LAURENTIAN OF THE OTTAWA DISTRICT* 



BY R. W. ELLS 



(Read before the Society December 29, 1892) 



CONTENTS 



Page 



Views of earlier Writers 349 



Present View 350 



Earlier Divisions of the Laurentian 351 



Scope of the present Paper 351 



The Laurentian Limestone and Gneiss 351 



Origin of the Term Laurentian 352 



Sir W. Logan's Investigation of the Laurentian Structure 352 



Summary of Sir W. Logan's Laurentian Section 353 



Eecent Investigations necessitate Change in the Section 854 



The Anorthosite Masses north of Saint Jerome 354 



Tremhling Mountain Section reexamined 354 



Region between Anorthosite Area and Gatineau River 355 



The Laurentian Gneiss and Limestone . . : 356 



Their Thickness 356 



Their stratigraphic Relation 357 



Their physical Characteristics 357 



Associated intrusive Rocks 358 



Resume' and Conclusions 359 



Views of earlier AYriters. 



In discussing the structure of the Laurentian rocks, as developed in 

 the valley of the Ottawa river, their characteristics, as given in the first 

 report of the late Sir William Logan, in 1845-'46, on " The Laurentian 

 of the Upper Ottawa," may here be presented. After stating that a low 

 anticlinal crosses that river between the mouth of the Mattawa and the 

 foot of Lake Temiscamingue, he says : 



" The lowest rocks which this undulation brings to the surface are of a highly 

 crystalline quality belonging to the order which in the nomenclature of Lyell is 

 called metamorphie instead of primary, as possessing an aspect inducing the theo- 

 retic belief that they may be ancient sedimentary formations in an altered condi- 



* Published by permission of the Director of the Geological Survey of Canada. 

 LII-Bull. Okoi,. Soc. Am., Vol 4, 1892. (349) 



