But we are making slow progress with our intended exposition of Mr Scrope's beautiful and instructive volume. Although salmon and salmon streams form the subject and "main region of his song," he yet touches truthfully, albeit with brevity, upon the kindred nature of sea-trout, which are of two species--the salmon-trout and the bull-trout. The fry of the former, called orange fins, (which, like the genuine parr, remain two continuous years in the river,) greatly resemble the young of the common fresh-water trout. "Like the grilse, it returns to the river the summer of its spring migration, weighing about a pound and a half upon an average."--P. 63. We think our author rather over-estimates their weight at this early period. Herlings (for so they are also named on their first ascent from the sea) rarely weigh one pound, unless they remain for a longer time than usual in salt water. In this state they bear the same relation to adult sea-trout as grilse do to salmon, and they spawn while herlings. They afterwards increase about a pound and a half annually, and in the summer of their sixth year (from the ovum) have been found to weigh six pounds.[16] Whether this is their ordinary ultimate term of increase, or whether, having every year to pass up and down the dangerous, because clear and shallow waters, exposed to many mischances, and, it may be, the "imminent deadly breach" of the cruive-dyke, and thus perish in their prime, we cannot say: but this we know, that they are rarely ever met with above the weight of six or seven pounds. [Footnote 16: See Mr Shaw's paper "On the Growth and Migration of the Sea-trout of the Solway."--_Transactions of the Royal Society of Edinburgh_. Vol. XV. Part iii. p. 369.] Of the generation and growth of the other and greater sea-trout (_Salmo eriox_,) we have not yet acquired the same precise knowledge, but its history may fairly be inferred to be extremely similar.