GRENVILLE SERIES OF EASTERN NORTH AMERICA 623 

 THE HALIBURTON-BANCROFT AREA IN EASTERN ONTARIO 



The Haliburton-Bancroft area in eastern Ontario, the mapping 

 of which has just been completed, occupies a position on the margin 

 of the protaxis corresponding to that of the ''Original Laurentian 

 Area" but is some 175 miles further west. It is very similar in 

 petrographical character to Logan's area but presents a somewhat 

 greater variety of rock types, the distribution of twenty different rock 

 types being represented on the Bancroft sheet accompanying the 

 report on the area in question. 



The Grenville series in this area presents a diversified series of 

 undoubted stratified rocks among which limestones preponderate, 

 but they rest upon and are invaded by an enormous body of gneissic 

 granite. 



To the southeast, toward the margin of the Paleozoic cover, the 

 sedimentary series is largely developed and is comparatively free from 

 igneous intrusions. Toward the northwest, however, the granite, 

 in ever increasing amount, arches up the sedimentary series and wells 

 up through it, in places disintegrating it into a breccia composed of 

 shreds and patches of the invaded rock scattered through the invad- 

 ing granite, until eventually connected areas of the sedimentary 

 series disappear entirely and over hundreds of square miles the 

 granite and granite gneiss alone are seen, holding, however, in almost 

 every exposure, inclusions which represent the last scattered remnants 

 of the invaded rocks. 



The type of structure presented by the invading granite is that 

 of a bathylith. 



The limestones. — The limestones in this Laurentian district are 

 very thick and underlie a large part of the area. In their more altered 

 form they exactly resemble those described by Logan in the areas 

 examined by him, but to the southeast of the Bancroft sheet, where 

 the invading granite is less abundant and the alteration of the invaded 

 strata is correspondingly less pronounced, the limestones appear in 

 less-altered forms and eventually pass into fine-grained, grayish-blue 

 varieties in which the bedding is perfectly preserved and concerning 

 whose truly sedimentary character there can be absolutely no doubt. 

 The gradual transition of the comparatively unaltered bluish limestone 

 into the coarsely crystalline white marble takes place by the develop- 



