43 



Huronian. 



Laurentian. 



Grenville. 



Exposures of the Huronian are to be seen along the 

 north shore and on numerous islands westward from 

 the vicinity of Killarney. Bell has mapped the rocks of 

 this age in two series — a lower series, "sericite, chlorite, 

 hornblende, and arkose- schists, clay slates, greywackes, 

 quartzites bands and dolomites" , and an upper series con- 

 sisting of quartzites. 



The quartzites form prominent ridges with a general 

 east and west direction which constitute a striking physio- 

 graphic feature of this part of the north shore. Near 

 Killarney an altitude of 1385 feet (421 m.) is attained and 

 even greater heights are reached a short distance inland. 

 Both series of the Huronian are invaded by numerous 

 masses of diabase, diorite and granite which afford inter- 

 esting contact phenomena. 



The gneisses and gneissoid granites of the Laurentian 

 form most of the shore of Georgian bay from Killarney to 

 the Palaeozoic contact at its southern end. The continuity of 

 this series is interrupted, however, near Parry Sound by a 

 band of Grenville rocks with which some interesting erup- 

 tives are asssociated. 



ANNOTATED GUIDE. 



Lake Ontario — Alt. 244-99 ft. ; 74-37 m. Lake 



Ontar i o 

 is 193 miles (310-8 km.) long, 53 miles (85-3 km.) wide 

 and 7,450 square miles (19,310 sq. km.) in area. The mean 

 elevation is 244-99 f eet (74 '37 m -) an d the maximum 

 depth 738 feet (224-9 km.). The north shore of the lake, 

 in the vicinity of Toronto, consists largely of sand, but 

 bold cliffs of glacial material face the lake to the eastward 

 of the city at Scarborough Heights, where one of the 

 finest glacial sections in the world is presented. (See 

 Guide Book to Excursion B-2). Toronto island has been 

 formed by debris swept westward from these heights by a 

 current which sets along the north shore. 



To the west of the city a few exposures of Lorraine 

 shales occur at the water level. The red shales of the 



