88 THE ROYAL SOCIETY OF CANADA 



Breccias and Associated Dyke. — -Half a mile to the northwest of 

 this basaltic exposure, there are two knolls roughly elliptical in 

 outline which are underlain in part by breccias similar in character 

 to those at La Trappe and the other localities described by Harvie. 

 These knolls are each about 150 yards long by 80 yards wide and the 

 underlying rocks are generally masked by a blanket of drift. On 

 the northern portions of these hills, there are several outcrops of 

 breccia, and a smaller knoll similarly underlain lies about fifty yards 

 to the northeast of the southern hill and along the strike of the 

 outcrops of breccia on the latter knoll. 



The included fragments are mainly of limestone, but as no fossils 

 were found, no definite information as to the age of these inclusions 

 can be given. Fragments of Laurentian granites and gneisses are 

 also present and must have been brought up from a considerable depth, 

 as the surrounding country is underlain by the Calciferous formation. 

 In this connection, it is noteworthy that the breccias at La Trappe 

 cut the Laurentian and contain fragments of the Potsdam sandstone 

 and Calciferous limestone, and, therefore, there must have been a great 

 deal of movement within the magma in both directions before final 

 solidification. 



The paste of the northern breccia has been almost entirely altered 

 to calcite and secondary quartz, and very little can be determined 

 concerning its original composition. Fragments of feldspars of very 

 different composition are present. These include Abi Ans, Abs An4, 

 and Ab4 Ana. Most of these are probably fragments of included 

 igneous rocks and not constituents of the magma itself. 



In the paste of the southern breccia there are feldspar grains 

 ranging from albite to labradorite so that it is impossible to state 

 which are constituents of the magma and which are inclusions. The 

 paste is very highly altered to calcite and secondary quartz, while 

 grains of black iron ore and very irregular flakes of a light-brown bio- 

 tite are also present. These flakes resemble the biotite of the alnoitic 

 occurrences much more closely than the neighbouring fourchite ex- 

 posure of Ste. Dorothée. 



On the west side of the road from Ste. Dorothée to St. Eustache, 

 about two miles from the former village, there is a quarry in the Calci- 

 ferous limestone. This limestone is here traversed by a highly 

 altered dyke about one foot in width. The only mineral which is 

 distinguishable in the hand specimen is calcite, as the rock as a whole 

 has been obscured by hydrous iron oxides. 



The minerals of which this dyke was originally composed cannot 

 be distinguished by means of the microscope, as it has been rendered 



