68 PRESIDENT’S ADDRESS—SECTION C. 
as the object of this address is to place before you the present 
state of our knowledge on this fundamental problem of geology, 
it will be as well for me to commence by describing shortly the 
principal facts connected with the movements—that is, the 
principal phenomena which have to be explained. 
PHENOMENA CONNECTED WITH THE MOVEMENTS. 
When we examine those portions of land which have been 
most elevated, we easily recognise two types-of structure. One 
is the Plateau type, in which the sedimentary rocks are nearly 
horizontal, and the only igneous rocks are overflows of basalt. 
The other is the Mountain Range or Alpine type, in which we 
find a granitic or gneissic core, surrounded by sedimentary rocks 
which have been plicated, and sometimes pushed horizontally 
over one another ; and here basalts are not commonly found in 
the mountains, but often occur at a little distance from them. 
The first of these types is evidently due to vertical uplift alone, 
the second to vertical uplift accompanied by lateral pressure. 
But the two types are connected by the Uinta and Park Ranges, 
the former being only a flattened dome, the second a dome into 
which granite and gneiss have been pushed, and the surrounding 
sedimentary rocks plicated or placed nearly vertical. The Andes 
forms another type of mountains, differing from the ordinary 
Alpine type by the addition of volcanoes along the centre of the 
range. The Caucasus is intermediate between the Alpine and 
Andean types, the central peaks of Elburz and Kazbec being 
extinct Andesitic volcanoes, surrounded by mountains of granite. 
What is known as the Jura type appears to be found only 
in mountains forming the outworks of a range on the Alpine 
type, and is not an independent structure. The Park Range also 
shows folds like the Jura. 
Depression of rock masses has occurred on an enormous scale, 
but we cannot examine the structure of the depressed rocks until 
they have been re-elevated. They all appear, however, to belong 
to one type, which corresponds to that of the plateau or regional 
uplift. I am not aware of any reason for supposing that folding 
of rocks ever took place with depression, or that any subsidences 
were accompanied by lateral pressure. There are, however, many 
reasons for thinking that neither elevation nor depression are 
continuous movements, but that both are irregular, sometimes being 
even reversed for short intervals, and thus giving rise to oscillations. 
Plications are always connected with great thickness of the 
plicated beds—that is, they never take place except after heavy 
sedimentation : a fact first pointed out by Professor James Hall 
of New York, and since confirmed in many parts of the world. 
For example, the older Paleeozoic rocks are very thick in Britain, 
and thin out easterly through southern Scandinavia, the Gulf of 
