28 



notably the relatively high upland tract lying to the south 

 of the town of Barrie, are gently undulating, nearly fiat, 

 till plains characterized by numerous small depressions. 

 The most notable exception to the prevailing "drum- 

 linized" and till plain surface is the range of hills which 

 lies about midway between the towns of Barrie and Orillia 

 and from 7 to 10 miles (11 to 16 km.) west of the ake. 

 These hills, the highest of which rises to an altitude of 

 nearly 600 feet (182.9 m -) above Lake Simcoe, are com- 

 posed, in greater part, of a loose sandy till partially strati- 

 fied. They are, in part morainic in character and appear 

 to have been formed during the retreat of the last ice 

 sheet. 



The greater portion of the area of Lake Simcoe district 

 is underlain by limestones of the Trenton, Black River 

 and Lowville formations (Ordovician), the last of which 

 rests unconformably on Pre-Cambrian crystalline locks. 

 The limestones dip gently towards the southwest at a rate 

 generally not exceeding 25 feet (7 . 6 m.) per mile, and have 

 an estimated maximum thickness in the district of 550 

 feet (167.7 m -)- Eastward from the lake, the limestones 

 are often well exposed and form a rock divide between the 

 waters of Lake Simco and Trent valley. 



The northern portion of the district, including the 

 area surrounding the lower end of Lake Couchiching, is 

 occupied by Pre-Cambrian rocks. Near the contact of 

 the limestones with the Pre-Cambrian rocks, an escarp- 

 ment is generally developed, and fronting the escarpment, 

 and often at a considerable distance from it, are 

 numerous outliers of limestone, showing that the limestone, 

 at one time, extended far over the Pre-Cambrian rocks to 

 the north. 



ANNOTATED GUIDE. 



Miles and 

 Kilometres. 



o m. Toronto, (Union Station). Alt. 254.0 



o km. feet (77.4 m.). 



14.0 m. Thornhill. — Alt. 635 feet (193.5 m.). 



22 . 5 km. Leaving Toronto the railway passes north- 

 ward over a series of drift hills and ridges 

 locally known as Oak Ridges which are, in 

 part, morainic in character, and extend for 



