On ascending them I found them to be two or three hundred feet high, and rising on their sides at an angle of 45 deg.
and on their tops, in some places for half a mile in length perfectly level, with a green turf, and corresponding exactly with the tabular hills spoken of above the Mandans, in plate 39, vol.1.I therein said that I should visit these hills on my way down the river; and I am fully convinced from close examination, that they are a part of the same original superstratum, which I therein described, though 7 or 800 miles separated from them.

They agree exactly in character, and also in the materials of which they are composed; and I believe that some unaccountable gorge of waters has swept away the intervening earth, leaving these solitary and isolated, though incontrovertible evidences, that the summit level of all this great valley, has at one time been where the level surface of these hills now is, two or three hundred feet above what is now denominated the summit level."-- Catlin's American Indians, Vol.2.pp.11 and 12.] [Note 35: Similar banks of fossil shells and oyster beds, are found in the Arkansas .-- Vide Catlin, Vol.2.p.85.At page 86, Mr.Catlin describes banks of gypsum and salt, extending through a considerable extent of country, and which apparently was of a very similar formation to some of the localities I was in to the north of Spencer's Gulf.] I have already observed that several circumstances connected with my own personal experience have led me to the conclusion, that there is no inland sea now occupying the centre of New Holland; it will be sufficient to name three of the most important of these.
First.

I may mention the hot winds which in South Australia, or opposite the centre of the continent, always blow from the north, to those, who have experienced the oppressive and scorching influence of these winds, which can only be compared to the fiery and withering blasts from a heated furnace, I need hardly point out that there is little probability that such winds can have been wafted over a large expanse of water.
Secondly.

I may state that between the Darling river and the head of the Great Australian Bight, I have at various points come into friendly communication with the Aborigines inhabiting the outskirts of the interior, and from them I have invariably learnt that they know of no large body of water inland, fresh or salt; that there were neither trees nor ranges, but that all was an arid waste so far as they were accustomed to travel.
Thirdly.

I infer the non-existence of an inland sea, from the coincidence observable in the physical appearance, customs, character, and pursuits of the Aborigines at opposite points of the continent, whilst no such coincidence exists along the intervening lines of coast connecting those points.
With respect to the first consideration, it is unnecessary to add further remark; as regards the second, I may state, that although I may sometimes not have met with natives at those precise spots which might have been best suited for making inquiry, or although I may sometimes have had a difficulty in explaining myself to, or in understanding a people whose language I did not comprehend; yet such has not always been the case, and on many occasions I have had intercourse with natives at favourable positions, and have been able, quite intelligibly, to carry on any inquiries.