38 COMMISSIONOFCONSERVATION 



Snowdon and Glamorgan into Dysart, where it is interrupted, and 

 then continues to the great northern mass of granite. The last two 

 lines are composed of granite and related rock, the former averaging 

 about ID and the latter 8 miles in width. These two, as well as the east- 

 em outcrop of volcanic rocks are surroimded by transformed sedi- 

 mentary rocks. This sedimentary rock being softer, many of the 

 stream valleys lie in it. This is notably the case with Deer creek, 

 Jcick creek, Eels brook, Irondale river, and Gull river for the greater 

 part of its length. The rocks described above belong to what the geo- 

 logists call the Grenville-Hastings series of the Palaeozoic Era. 



Sedimentary limestone of a different geological age (Cambro- 

 Silurian) occurs in southern Marmora in a large block, continuing in 

 '-mattered patches westward to central Harvey, where it extends with 

 some intrusions of other kinds of rock, in a northwest direction through 

 southern Galway and nearly diagonally through Somerville to the limits 

 of the watershed. 



i Sails. — The region has suffered severely from glaciation, and the 

 nature of the soils has been determined by it and by the excessive 

 flow of waters during and immediately subsequent to the ice age. 

 Many of the ridges were scoured clean of their soils, and the elapsed time 

 since has not been long enough to restore them by natiu-al processes 

 to more than a very shallow depth. The killing of the protecting 

 trees and the destruction of the humus by fires have resulted in washing 

 off the soil in many cases, especially on the granite, so that now the 

 ridges are bare. The rock of the low ridges and upland areas is covered 

 by a thin mantle of glacial debris, mostly sand, gravel, and pebbles. 

 It is rarely that one finds the soil on the uplands more than i8 inches 

 deep, except in local pockets. This applies to farm lands, as well 

 as to the forest lands. The flats between the low ridges have, at one 

 time, been covered by glacial waters, and the debris has been more or 

 less sorted, but the top layer of soil is sand interspersed with thin 

 layers of gravel. These are the areas which were originally occupied 

 by pine, and, unfortunately, they are now often occupied by farms. 

 The stream valleys were filled with glacial drift and the present streams 

 have worn their channels through it, forming sandy terraces along the 

 slopes. In the western portion of the watershed particularly, most of 

 the farms are in the stream valleys. The lower terraces, and especially 

 the flood plains, contain, indeed, fairly good agricultural soil, but these 

 areas are very limited in extent except in the lower courses of the 

 larger streams. 



As a whole, the soils of the area may be roughly grouped into three 

 classes, which in sequence of their abundance are : stony, light, sandy 



