375 



these ancient traps are diorites (or diabases in some 

 instances) with an ellipsoidal or pillow structure. In 

 places that have been badly weathered, this structure is 

 sometimes obscured, but careful search will usually reveal 

 it even when the trap has been largely altered to chlorite 

 schist. The ellipses 'usually consist of a light coloured 



•■'a ',: ? 



Contact breccia, Keewatin and Laurentian. Barry lake. 



interior and an outer band of dark material which appears 

 to be a basic segregation, though both portions can be 

 classed as diorite. In the interstices between the ellipses 

 is a filling of ferro-dolomite or ankerite with some quartz and 

 frequently a considerable quantity of epidote. Rocks of 

 this character are particularly well shown at Devil's Gap 

 and on the west side of Big Stone bay from the Keewatin 

 mine to Eagle passage. In these places the typical 

 ellipsoidal structure is well developed. In other places the 

 squeezing of these ellipses in the alteration of the rock to 

 chlorite schist and in certain instances to sericite schist 

 is beautifully shown. 



At the contact of the Keewatin with the Laurentian 

 there is found usually, if not always, a hornblendic rock 



