Davis and Wood.] 
376 
[Nov. 20, 
plain some indications of its origin according to the above crite- 
ria, and in sucli work contoured maps are essential. They have a 
quantitative accuracy, while shaded or hachured maps give only a 
qualitative idea of form. It would be quite impossible to carry on 
careful geographic study without the knowledge of height, such as 
contours give, as well as of length and breadth ; for the study of 
the form of the land is a study of three dimensions. The contoured 
map of New Jersey is invaluable in this regard. 
10. A restoration of part of the old Highland peneplain was 
made by copying from the contoured maps on a sheet of tracing pa- 
per the heights of all the broad, topmost elevations of the plateau 
divides between the streams. The principle has already been stated 
that the valleys, which have been deepened quickly in a geographic 
sense, were once almost as high as the interstream plateaus, which 
must have wasted away much slower ; and this warrants our be- 
lieving that the interstream elevations may be taken as giving 
some indication of the form of the surface before the valleys were 
made. Contours are drawn on the tracing paper in accordance 
with these elevations, and a fair map of the old Highland peneplain 
is thus constructed. It should be noted that the restoration thus 
secured may have somewhat less relief than the old plain possessed ; 
for it is only a generalization, on which much detail is lost. The old 
plain is at once seen to be broadly undulating, and the undulations 
seem to be too strong to be considered as belonging to an ancient 
submarine platform. The plain is therefore best regarded as an area 
of subaerial denudation, not entirely worn down to the ultimate 
form of an absolute plain, but reduced from a mountainous matu- 
rity to very mild relief in its old age. 
The penultimate stage of subaerial denudation would give essen- 
tially such a surface as has been discovered in our restoration. It 
ma}^, however, be suggested that the old surface was a true sub- 
marine platform, subsequently somewhat deformed, perhaps at the 
time of general elevation. To this it can hardly be answered that 
no traces of the platform sediments have been found on the plateau, 
for they might easily have been swept away during the excavation 
of the deep and wide valleys that now traverse the Highlands ; but 
it may be fairly argued that a final subaerial baselevel plain could 
be similarly distorted ; and it may be strongly urged that, since the 
higher parts of the restored surface coincide with the areas of harder 
rocks, as the penultimate elevations of an old baselevelled area must, 
