About thirteen miles below Rum River, and when within half a mile of the Falls,[86] I observed calcareous rocks in horizontal beds, on the left bank of the river. It was now evident we had passed out of the primitive range of deposits, and had entered that of the great sedimentary horizontal and semi-crystalline or silurian system of the Mississippi Valley; and descending with a strong current, we came, rather suddenly, it appeared, to the Falls of St. Anthony, where the river drops, by a cascade, into a rock-bordered valley. Surprise and admiration were the first emotions on getting out of our canoes and gazing on this superlative scene; and we were not a little struck with the idea that the Sioux had named the Falls from manifestly similar impressions, calling it Rara, from the Dacota verb _irara_, to laugh. By another authority, the word is written _Ha Ha_, or _Dhaha_, the letters _h_ in the word representing a strong guttural sound resembling the old Arabic r.[87] (S. R. Riggs's _Dakota Dict. and Gram._) Nothing can exceed the sylvan beauty of the country which is here thrown before the eye; and we should not feel surprised that the Aboriginal mind has fallen on very nearly identical sounds with the English, to express its impressions. A not very dissimilar principle has been observed by the Chippewas, who have a uniform termination of their names in _ish_, which signifies the very same quality which we express by ish in whitish, blackish, saltish--meaning a lesser, or defective quality of the noun. [86] It is recently asserted that this change in the stratification occurs about a mile above the Falls. [_Sen. Doc._ p. 237.] By the same authority it is shown that the aggregate fall of the Mississippi from the mouth of Sandy Lake River to the Falls of St. Anthony is 397 feet. [87] Both words are derived from the verb _to laugh_.