VULCANISM AND MOUNTAIN-MAKING 169 
the diastrophism went somewhat deeper and lifting was relatively 
more important. Asa part of the Jurasside orogeny which devel- 
oped the Sierra Nevada Range, powerful overthrusting occurred far 
to the east of these mountains. But in these areas of overthrusting 
igneous activity contemporaneous with the diastrophism seems to 
have been unimportant. 
The extraordinary Caledonian diastrophism affected both the 
British Isles and Scandinavia. In the Scottish Highlands on the 
western border the planes of overthrusting dip eastward under the 
deformed belt; in Scandinavia they dip westward likewise beneath 
the strongly deformed belt. Singly, each case illustrates the prin- 
ciple of bordering thrust faults on the outer margins of compressed 
mountain ranges? Together, Scottish thrusts on the west and 
Scandinavian thrusts on the east, they constitute seemingly a wedge 
similar to the Appalachian wedge of Pennsylvania.’ 
The region of these extraordinary Caledonian overthrusts in 
the Northwest Highlands of Scotland seems to have been essentially 
free from igneous phenomena during the time of the vigorous de- 
formation. Such intrusions as took place at this time were located 
off to the southeast, especially in the Ochil and Sidlaw Hills® and 
the Cheviot district, which are near the middle of the deformed 
belt far from the overthrust border. During the deposition of the 
Lower Old Red Sandstone which followed the Caledonian dis- 
_ turbance, large quantities of volcanics were poured out in the 
central Lowlands between the base of the Highland Mountains 
and the Uplands of the southern counties.° But no undoubted 
vents of Lower Old Red Sandstone age have been detected 
C. R. Longwell, ‘“‘Geology of the Muddy Mountains, Nevada, with a Section 
to the Grand Wash Cliffs in Western Arizona,’ Am. Jour. Sci., Fifth Series, Vol. I 
(1921), pp. 39-62; E. S. Bastin, personal communication. 
2“The Building of the Colorado Rockies,”’ Jour. of Geol., Vol. XXVIII (1910), 
PP- 243, 240. 
3Rollin T. Chamberlin, ‘“The Appalachian Folds of Central Pennsylvania,” 
Jour. of Geol., Vol. XVIII (1910), pp. 228-51. © 
4“The Geological Structure of the Northwest Highlands of Scotland,” Mem. 
Geol. Surv. of Great Britain (1907). 
5 Sir Archibald Geikie, Ancient Volcanoes of Great Britain, Vol. I (1807), pp. 
277-79: : 
S7bid., pp. 271-72; 205-335. 
