ulf into which they have
flowed for many ages.[5]

"The division, which has here forced itself upon our notice, between the
Upper and the Lower Mesopotamian country, is one very necessary to engage
our attention in connection with ancient Chaldaea. There is no reason to
think that the term Chaldaea had at any time the extensive signification of
Mesopotamia, much less that it applied to the entire flat country between
the desert and the mountains. Chaldaea was not the whole, but a part, of the
great Mesopotamian plain; which was ample enough to contain within it three
or four considerable monarchies. According to the combined testimony of
geographers and historians,[6] Chaldaea lay towards the south, for it
bordered upon the Persian Gulf, and towards the west, for it adjoined
Arabia. If we are called upon to fix more accurately its boundaries, which,
like those of most countries without strong natural frontiers, suffered
many fluctuations, we are perhaps entitled to say that the Persian Gulf on
the south, the Tigris on the east, the Arabian desert on the west, and the
limit between Upper and Lower Mesopotamia on the north, formed the natural
bounds, which were never greatly exceeded, and never much infringed upon.
These boundaries are for the most part tolerably clear, though the northern
only is invariable. Natural causes, hereafter to be mentioned more
particularly, are perpetually varying the course of the Tigris, the shore
of the Persian Gulf and the line of demarcation between the sands of Arabia
and the verdure of the Euphrates valley. But nature has set a permanent
mark, half way down the Mesopotamian lowland, by a difference of a
geological structure, which is very conspicuous. Near Hit on the Euphrates,
and a little below Samarah on the Tigris,[7] the traveller who descends the
streams, bids adieu to a somewhat waving and slightly elevated plain of
secondary formation, and enters on the dead flat and low level of the new
alluvium. The line thus formed is marked and invariable; it constitutes the
only natural division between the upper and lower portions of the valley;
and both probability and history point to it as the actual boundary between
Chaldaea and her northern neighbour."[8]

Whether the two States had independent and separate life, or whether, as in
after years, one of the two had, by its political and military superiority
reduced the other to the condition of a vassal, the line of demarcation was
const