1889.] 
373 
[Davis and Wood. 
the antecedent form may be restored, with sufficient accuracy for 
our purpose, by filling up the valleys nearly to the height of the 
uplands between them, as Professor Cook suggested ; and it is 
manifest from an examination of the maps or from a view of the 
country, that the restoration would be abroad surface of very gen- 
tle undulation, so smooth that we may call it almost a plain, that 
is, a peneplain. 1 It is then from such an old peneplain surface 
that the present rugged Highlands have been carved. The old pene- 
plain remains but slightly attacked on the interstream plateaus, 
such as the broad summit of Scliooley’s mountain ; its destruction 
has been carried farthest on the softer rocks, where the valle}^s have 
been deepened and widened. 
7. Origin of the old Highland peneplain. How could the old 
plain surface of the uplands originate? It was not a construc- 
tional plain, like that of the Red river of the north, between Min- 
nesota and Dakota, for there is no reason to suppose that it was ever 
by any means perfectly level. The rocks of the Highlands are chiefly 
.crystalline gneisses and schists, with slates and limestones, all greatly 
disturbed ; 2 if there be any truth in the prevailing theories that ac- 
count for the present condition of such rocks, both the formation 
of most of them and the deformation of all must be ascribed to 
processes working at depths of thousands of feet below the surface 
of the earth. Moreover, the folia of the gneisses and schists and 
the strata of the bedded rocks northwest of them are commonly 
seen standing at steep angles, and their present outcropping edges 
manifestly do not mark their original extension. It must, there- 
fore, be surely concluded that the old upland peneplain was not the 
original constructional surface of the underlying rocks, but was a 
surface produced by the action of destructive forces on a once much 
larger mass. It remains to be seen why a tolerably even surface 
was produced by these destructive forces. 
Examples may be quoted in plenty from the region of the western 
plateaus to show that destructive forces produce even surfaces when 
they denude a cover of softer rocks and encounter a hard stratum ; 
but, in such case, the hard stratum must be horizontal. The pene- 
plain of the Highlands cannot be explained in this way, for its rocks 
are strongly tilted, as has been stated above. The peneplain had 
1 This term was used by the senior author in describing the restored forms of the up- 
lands in Connecticut, which are believed to be of the same age as those here consid- 
ered. Amer. Journ. Science, xxxvii, 1889, 430. 
2 Ann. Rep. Geol. Surv., N. J., 1884, 44; 1886, 89, 119. 
