180 ROYAL SOCIETY OF CANADA 
limestone and associated stratified gneiss, and consequently of more recent 
date. These examinations extended over several years and embraced large 
areas both to the north of Montreal and in the Quebec and Lake St. John 
district, and the results arrived at by Dr. Adams as to their eruptive 
character, based upon an exhaustive study, both in the field and by the 
aid of the microscope, must be taken as conclusive on this subject.’ Thus 
the study of the Laurentians both on the extreme east and west of the 
typical area has strongly tended to establish the opinion that many of the 
usually accepted views as to the structure and origin of the syenitic and 
granitic gneiss and of other portions of the great Archean complex 
require to be very considerably modified. 
In the consideration of a question of such great extent and of such 
complexity as that of the origin and structure of these ancient crystallines 
presenting as they do such variety in composition and physical character, 
with such diversity of relations, it is to be feared that much of the 
apparent discrepancy of opinion has arisen from the attempt to solve the 
problem by a study of too limited an area, or from a too rapid generaliz- 
ation from insufficient data, too often obtained from unreliable sources 
The methods of study of the older crystallines and eruptives also have 
materially changed during the last twenty years ; and the revelations of 
the microscope have thrown much light upon questions which for a long 
time were perplexing in the extreme. Thus it has gradually come about 
that much of what, in the early days of the study of this series of rocks, 
was considered from their physical characters, chiefly of aqueous ori- 
gin, has been clearly shown to have originated in an entirely different 
manner, and that many of these rocks, formerly supposed to be sedimen- 
tary, are, in fact, truly igneous masses. While many differing views have 
been expressed by the several workers in this very interesting geological 
field, it may be stated that the Grenville series or the original typical 
Laurentian area of Logan probably most fully illustrates the most per- 
fect section of the Laurentian rocks which we can yet recognize. This 
section embraces a great variety of rock structure. It includes the 
various kinds of gneiss, foliated and stratified, with foliated and massive 
granites and syenites, pyroxenic and dioritic, hornblende and quartzose 
rocks, quartzite and limestone. In the basal beds of the latter are interstra- 
tified bands of rusty quartzose gneiss which, from the evidence yet at our 
disposal, form an integral part of the calcareous formation. This portion 
presents in its banded arrangement of quartzose and calcareous rocks, the 
usual aspect of true altered sedimentary strata. The same well banded 
arrangement is also visible in some of the directly underlying gneiss ; but 
in the case of the great mass of this gneiss, the microscopic examination 
shows the evidence of an aqueous origin to be wanting. Whatever may 

1  [eber das Norian oder Ober-Laurentian von Canada” aus dem Neues Yahr- 
bach für Minerologie, etc., Beilageband, VIII., Stuttgart, 1893. 
