PRESIDENT’S ADDRESS—-SECTION C. 69 
Finland, and northern Russia. Before the Devonian period they 
were much folded in Britain, but in Russia they remain horizontal 
to the present day. In the Ural Mountains, however, they were 
covered by heavy carboniferous deposits, and here they were 
disturbed immediately after the Carboniferous period. In the 
peninsula of India the Bijawan series is horizontal where thin, 
and much folded where thick. The Star formation in Queensland 
is only some 1200 feet thick in the Star gold-field, and is here 
but little disturbed; while in the Hodgkinson and Palmer 
gold-fields, where itis more than 21,000 feet thick, it is highly 
inclined. In North America, the Paleozoic sediments of Virginia 
and Pennsylvania in the east, and of Nevada in the west, are each 
about 40,000 feet thick and much disturbed ; but between them, 
in Colorado and the Mississippi valley, they get thin, and here 
they are horizontal. So with the Mesozoic rocks in the same 
region ; they also are only folded where they are thick. All the 
contorted beds of mountain ranges are parts of thick deposits. 
The elevation of the north-west Himalaya was preceded by the 
deposition of 30,000 feet of strata, that of the Swiss Alps by 
more than 30,000 feet, that of the Australian Alps by more 
than 35,000 feet, and that of the Appalachians by 40,000 feet. 
These examples are sufficient to show that only thick deposits 
are folded, but it does not appear that the plications are propor- 
tional to the thickness of the deposits, The folded Cretaceous 
rocks on the east base of the Rocky Mountains are not more 
than 12,000 feet thick, while the folded marine tertiaries of 
California are said to be only 4000 to 5000 feet thick. On 
the other hand the carbonaceous formations of New South 
Wales are more than 11,000 feet thick and not folded. The 
Gondwana system in the Raniganj coal-fields of India is 11,200 
feet, and in the Satpura basin it is even 22,500 feet thick and 
yet not folded. So also in North America, the tertiary beds 
of the Wahsatch and Uinta districts are 12,400 feet, and the 
conformable strata of the Colorado plateau are 10,000 to 15,000 
feet and yet not plicated. Evidently plication does not necessarily 
follow heavy sedimentation. 
Another important point is that plication is not universal. 
Some large regions of the earth’s surface have never been plicated 
since Archean times. I have already mentioned the Gulf of 
Finland. In Canada, Cambrian rocks, 2000 feet thick, lie hori- 
zontally on contorted Archeans, The Arvali Range in Rajputana 
is formed of plicated Archzean schists which have not since been 
disturbed, for the Vindhyan system, which is of lower Paleozoic 
age, is found in the neighbourhood in a nearly horizontal position ; 
indeed the Vindhyan system is horizontal over the greater part 
of the peninsula of India. 
The action which has caused plication has constantly shifted 
its position. As pointed out by J. D. Dana in 1846, a continent 
