of the advantage of constructing geological sections on a true scale 
as to the relative proportions of height and length.* 
Table-lands or Plateaux are elevated regions of flat or undulating 
country, rising to heights of 1000 feet and upwards above the level 
of the sea. hey are sometimes bordered with steep slopes, which 
descend from their edges, as the table-land of the Spanish peninsula 
does into the sea. In other cases they gradually sink into the plains 
and have no definite boundaries; thus the prairie land west of the 
Missouri slowly and imperceptibly ascends until it becomes a vast 
plateau from 4000 to 5000 feet above the sea. Occasionally a high 
table-land is encircled with lofty mountains, as in those of Quito 
and Titicaca among the Andes, and that of the heart of Asia; or it forms 
in itself the platform on which lines of mountains stand, as in North 
America, where the ranges included within the Rocky Mountains 
reach elevations of from 10,000 to 14,000 feet above the sea, but 
not more than from 5000 to 10,000 feet above the table-land. 
Two types of table-land structure may be observed. 1. Table- 
lands consisting of level or gently undulated sheets of rock, the 
general surface of the country corresponding with that of the — 
stratification. The Rocky Mountain plateau is an example of this 
type, which may be called that of Deposit, for the flat strata have 
been equably upraised nearly in the position in which they were 
deposited. 2. Table-lands formed out of contorted, crystalline, or 
other rocks, which have been planed down by superficial agents. 
This type, where the external form is independent of geological 
structure, may be termed that of Erosion. The fjelds of Norway are 
portions of such a table-land. In proportion to its antiquity, a plateau 
is trenched by running water into systems of valleys, until in the end it 
may lose its plateau character and pass into the second type of moun- 
tain ground above described. This change has largely altered the 
ancient table-land of Scandinavia, as will be illustrated in Book VII. 
Plains are tracts of lowland (under 1000 feet in height) which 
skirt the sea-board of the continents and stretch inland up the river 
valleys. ‘The largest plain in the world is that which, beginning in 
the centre of the British Islands, stretches across Europe and Asia. 
On the west it is bounded by the ancient table-lands of Scandinavia, 
Scotland, and Wales on the one hand, and those of Spain, France, 
and Germany on the other. Most ofits southern boundary is formed 
by the vast belt of high ground which spreads from Asia Minor 
to the east of Siberia. Its northern margin sinks beneath the 
waters of the Arctic Ocean. This vast region is divided into an — 
¥ 
4 
40 GEOGNOSY. "(Boom iL 


Z 
py 
eastern and western tract by the low chain of the Ural Mountains, — | 
south of which its general level sinks, until underneath the Caspian 
Sea it reaches a depression of about 3000 feet below sea-level. For 
several hundred miles southward from the Arctic Ocean traces of 
recent sea-shells are found in the superficial deposits. Similar 
' Sections and Views, illustrative of Geological Phenomena, 1830. Geol. Observer 
p. 6416, 
