390 SURFACE GEOLOGY, PICTOU COAL FIELD—POOLE, 
And at such places the extent of the denudation, where not 
only has the boulder clay been washed away, but the older for- 
mations have been further eroded, may be taken as some gauge 
of the time since the present condition of things began. 
One of the more convincing evidences of the glacial character 
of these ridges is a depression perfectly straight from the slightly 
raised centre of which water flows, when there is any to flow in 
diametrically opposite directions. 
To the mineral explorer a knowledge of the nature of these 
deposits leads him to sink his trial pits in the lower ground 
where he may expect to find the surface offer less depth than on 
the crest of the ridges, and this knowledge is of no small value 
in the field under review since the excessive thickness of the 
diluvium is in many parts a great bar to the study of the 
structure of the older rocks beneath. 
Twenty and thirty feet is a common depth, while sinkings 
sixty and even eighty-six feet have failed to pierce these deposits. 
The deepest spots are where it is supposed the river and larger 
brooks at one time ran previous to the deposition of the drift. 
The position of these beds of drift is also a matter of no small 
worth to the Railway contractor, for there have been several 
instances where men accustomed to the soil of other sections of 
country have been disagreeably surprised to find the cost of 
earthwork in Nova Scotia far exceeded their estimates and 
experience elsewhere. 
After the agreement in 1858 between the Local Government 
and the General Mining Association threw open the unreserved 
mineral lands to other lessees, an endeavor was made to trace the 
coal beds outside the Association’s areas, but beyond a few chains 
distant this endeavor to the westward was for many years a fail- 
ure. West of a certain line, the depth of the surface material 
was found to suddenly increase, and several trial pits and bore- 
holes were abandoned when they failed to reach the rock at forty 
feet and more. This western limit of shallow drift probably indi- 
cates the eastern bank of McCulloch’s brook in pre-glacial times, 
and studied in the light of our present knowledge of the under- 
lying strata, it marks also the eastern side of the McCulloch’s 
