54 THE ROYAL SOCIETY OF CANADA 



The paste of which these breccias are composed is, as a general 

 rule, alnoitic in character, and it is, therefore, natural to expect occur- 

 rences of alnoite near by. This is indeed the case, as at several 

 localities to the west of Montreal there are intrusions of alnoite. 

 As these occurrences are described more fully below, it is unnecessary 

 to refer to them further at this point. 



The fact that these breccias and minor alnoite intrusions are 

 found to the west of St. Bruno and in increasing number to the west 

 ■of Mount Royal might indicate that they are also present in connec- 

 tion with the other intrusions, but have not yet been discovered. On 

 the other hand, it is observed that the western members of the main 

 series of intrusives were, in all probability, active volcanoes, whereas 

 the eastern members are laccolithic in character, and, therefore, it 

 might be expected that the magma was much closer to the surface at 

 the west than towards the east and that these minor intrusions have 

 accompanied volcanic activity in an area whose overburden was 

 comparatively light, compared with that above, let us say, Shefford 

 and Brome. However, this thickness must have been considerable 

 even at Mount Royal as the Lorraine alone attains a thickness of over 

 2,000 feet, and the Oriskany must have been considerably above that 

 formation. 



On the other hand, the western intrusives are found to be more 

 basic in character than those towards the east, and these basic mag- 

 mas, being more fluid than the acid magmas, may have been able to 

 penetrate the rocks much more easily, both laterally and vertically, 

 and thus give rise to these outliers and also to such phenomena as the 

 intrusions of igneous breccia. 



Quaternary 



Pleistocene. — In glacial times the whole area was covered by a thick 

 mantle of boulder clay or unstratified glacial drift. 



After the glacial period, there was a period of submergence of 

 the St. Lawrence Valley to a height of approximately 690 feet during 

 which the morainic material was reworked and the Leda clay and the 

 Saxicava sand were deposited on the shores of the epi-continental 

 Champlain Sea. Uplift followed with a series of pauses, as is evi- 

 denced by the beaches found at various elevations around the City 

 of Montreal and the valley of the Ottawa River. 



Petrographical Descriptions 



Monticellite Alnoite, Como, Que. 



About one-half mile south-east of Como Station (29.9 miles from 

 Montreal on the Canadian Pacific Short Line to Ottawa) a low ellip- 



