116 CRUISE OF THE NEPTUNE 
than these Silurian limestones are not found south of Lancaster 
sound and Barrow strait, except on the northern part of Banks 
island at the extreme west of the archipelago. These rocks of 
Devonian and Carboniferous age occupy the Parry islands and 
the western and northern parts of Ellesmere, and in many 
places contain good deposits of coal. 
A yet newer series of rocks belonging to the Mesozoic are 
found along the western edge of Ellesmere and on the Sverdrup 
islands. Isolated patches of later Tertiary age probably also 
occur along the northern and eastern coasts of Baffin island, and 
are of importance in that they are often associated with deposits 
of lignite coal. Small areas of this age have been found in the 
Parry islands and on the western part of Banks island. 
On these northern islands the country underlain by the crys- 
talline archaean rocks is very similar in physical character to 
like areas of more southern regions. Where these rocks occur, 
the coast is usually greatly broken by irregularly shaped bays 
and headlands. The shores are often fringed with rocky 
islands, and the adjacent sea-bottom is liable to be very uneven. 
The land, as a rule, rises rapidly from the coast into an uneven 
plateau or tableland, whose general level is broken by ridges of 
rounded hills which seldom rise more than a few hundred feet 
above the general level. The elevation of the tableland varies 
from, a few hundred feet to an extreme height of nearly five 
thousand feet. 
In the northern parts the surface of this Archaean tableland 
is usually covered with a thick ice-cap, through which only the 
loftier hills protrude. The valleys leading down to the coast 
from the ice-cap are filled with large glaciers which project into 
the bays, where they discharge numerous icebergs. As the ice- 
cap becomes thinner in the more southern parts the glaciers 
become less active, and generally terminate without reach- 
ing the sea, and consequently no icebergs are formed from 
them. 
