STRUCTURAL RELATIONS OF PRE-CAMBRIAN AND PALAEOZOIC. 17 
This relationship of the two series of rocks occurs southeast of 
Madoc, where the Ordovician limestone on the south side of 
Moira lake forms an escarpment rising 150 feet above the lake 
and considerably higher than the granite area on the opposite 
side. Similar topographic relations between these two rock 
series exist northwest of Madoc and west of Belmont lake 
where the retreat of the Ordovician limestone through denuda- 
tion has left walls of cliffs standing higher than the adjacent 
Pre-Cambrian. These examples will suffice to show the markedly 
different types of topography which denudation has developed 
on very similar groups of rocks in areas which are geographically 
only slightly removed from each other. The differences are 
evidently to be explained by corresponding variations in the 
structure. The operation of ordinary processes of erosion 
alone will not explain the very different topographic features 
exhibited by the western and southeastern borders of the "Pro- 
taxis”. The escarpment-like border shown by the Archaean 
in the latter region can only be explained on the assumption 
that denudation has there been aided by profound faulting. 
Evidence which strongly corroborates, if it does not alone 
demonstrate, the validity of the inference of faulting, is furnished 
by the areal relations of the Palaeozoic and Pre-Cambrian. 
The contact of these two rock series along the Ottawa River 
valley has been mapped by the Geological Survey, Canada, 
on a scale of 4 miles to 1 inch, and the contact is there shown, 
throughout its course, as a straight or gently curving line. 
The Archaean area is nowhere invaded by tongues or projecting 
angles of Palaeozoic rocks such as would certainly be present 
if faulting had not substituted an approximately straight con- 
tact for the usual highly irregular contact resulting from the 
denudation of beds so unlike as the Archaean and Palaeozoic. 
The highly irregular type of contact which develops between these 
rock groups under normal conditions and in the absence of fault- 
ing is seen in the maps by Miller and Knight 1 showing the 
Palaeozoic- Archaean boundary in the region northwest of Kingston; 
but this irregular zigzag type of contact is unknown along the 
1 Rept. Ontario Bur. Mines, vol, XXII, pt. II, 1914. 
