^{page 1 note 1} The views contained in this paper, the sources of some of which will be obvious, were first expressed before the Halifax Philosophical Society, in a lecture which I delivered in 1874, and afterwards in a paper read before the Leeds Geologists' Association. They are now printed in a condensed form and rather as suggestions than anything else.

^{page 1 note 2} The increased amount of energy in the sun does not imply a corresponding elevation of temperature; to a great extent such additional energy was potential, but from all we know it seems most probable that an increase in potential would be accompanied in this case by an increase in kinetic energy, and so we may safely assume that the temperature of the sun rises in an ascending curve as we proceed backwards in time. The more rapid conversion of potential into kinetic energy, which probably occurred at intervals, would produce fluctuations in temperature, and so the temperature curve in the sun's history is probably not a simple line, but varied by numerous minor undulations.

^{page 1 note 3} The studious reader who desires to enter more fully into this question of the “Rate of Geological Change” should consult Prof. Huxley's Presidential Address to the Geological Society (1869), Quart. Journ. Geol. Soc., vol. xxv.; Prof. E. Forbes “On the Manifestation of Polarity in the Distribution of Organized Beings in Time” (Royal Inst. Lectures, vol. i. p. 428); Prof. Phillips' Rede Lecture: Cambridge, 1860, afterwards published by Macmillan under the title “Life on the Earth,” 1860; and an able article by Mr. H. M. Jenkins, F.G.S., Sec. Royal Agl. Soc. of England, “On the Rate of Geological Change,” Quart. Journ. Science, 1870, vol. vii. p. 322.—Edit. Geol. Mag.