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It will be necessary to enter more at large than in my preceding volumes into the resources of Canada, and, for this end, Geology and other scientific subjects must be introduced; but, as I dislike exceedingly that heavy and gaudy veil of learning, that embroidered science, with which modern taste conceals those secrets of Nature which have been so partially unfolded, I shall not have frequent recourse to absurd Greek derivations, which are very commonly borrowed for the occasion from technical dictionaries, or lent by a classical friend; but, whenever they must occur, the dictionary shall explain them, for I really think it beneath the dignity of the lights of modern Geology to talk as they do about the Placoids and the Ganoids, as the first created fishlike beings, and of the Ctenoids and the Cycloids as the more recent finners.
The "true Fishes" are divided by him into Ctenoids and Cycloids, according as the posterior margin of their scales is denticulated or smooth, a circumstance the importance of which to the animal must be infinitely small, in comparison to the peculiarities of the dentition, formation of the fins, number of vertebrae, etc.
"More than fifteen hundred species of fossil fishes, which I have learned to know, tell me that species do not pass insensibly one into another, but that they appear and disappear unexpectedly, without direct relations with their precursors; for I think no one will seriously pretend that the numerous types of Cycloids and Ctenoids, almost all of which are contemporaneous with one an other, have descended from the Placoids and Ganoids.
Underlying all its divisions and subdivisions, is the average expression of the type in the past and present; the Placoids and Ganoids, with their combination of reptilian and fishlike features, characterizing the earlier geological epochs, while in the later the simple bony fishes, the Cycloids and Ctenoids, take the ascendancy.
The action of a paddle wheel in the water resembles in this respect that of the wheel of a carriage running along the ground: that point in the radius of the paddle of which the rotative speed is just equal to the velocity of the vessel will describe a cycloid; points nearer the centre, prolate cycloids, and points further from the centre, curtate cycloids.
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