MAPS AS GEOGRAPHICAL ILLUSTRATIONS 493 
lands on the north and Southern Uplands on the other side. 
This series of sheets exhibits on the north the border of the 
eastern Grampians, which repeat the systemless, trendless forms 
of the Ben Nevis region; the sudden descent to the Lowlands, 
where the tilted rock structure produces well defined ridges of 
moderate height—not to be confused however with the numer- 
ous drumlins of smooth-flowing form and arrangement and of small 
elevation. The chief ridges are the Ochils, the Sidlaws, and the 
Pentland hills; these being resistent interbedded igneous rocks, 
Carboniferous for the most part, that have withstood the erosion 
of Tertiary time. The river Tay, emerging from the Gram- 
pians on the north, breaches the Sidlaws at Perth, and then turns 
eastward and follows the axis of the anticline, whose flanks 
form the Sidlaws on the north and eastern Ochils on the south 
to its estuary at Dundee. The Forth, breaching the Ochils at 
Sterling, turns eastward through its estuary or Firth in the broad 
depression between the Ochils and the Pentland Hills. To the 
southeast of Edinburgh, the preglacial surface of the Lowland 
appears to have been less degraded than aggraded by glacial 
action, for the district is completely fluted with drumlins. The 
smaller streams hereabouts all follow narrow postglacial channels 
The Southern Uplands rise in the Lammermuir group ; irregu- 
larly dissected, but of much less relief than the Highlands, and 
generally with smoothly flowing forms. 
The most important matter to emphasize in connection with 
this group is that the moderate altitude of the Lowlands is not 
due to failure of uplift hereabouts of the ancient lowland of 
denudation which embraced all Scotland; the district of the 
Lowlands was uplifted with the Highlands on the north and the 
Uplands on the south; but while the Highlands and Uplands have, 
in virtue of their resistant rocks, retained in their skylines good 
evidence of the altitude to which their entire surface formerly 
rose, the Lowlands, of relatively weak rocks, have wasted away 
and asa whole are reduced to an imperfect peneplain of the 
second generation. It is only where the more resistant volcanic 
rocks occur among the weaker sedimentaries that a significant 
