38 Proceedings of the Royal Physical Society. 



levels, and subsequently aids in concentrating it into 

 one bed."] 



The foregoing paragraphs, before those enclosed in square 

 brackets, contain a nearly verbatim report of an address I 

 gave before the Koyal Physical Society of Edinburgh at the 

 December meeting, 1894, without any addition or alteration. 

 The same address was also given before the Edinburgh 

 Association of Science and Art that year, and was awarded 

 their Diploma. A few weeks afterwards it was delivered 

 before the Carlisle Scientific Society at Tullie House ; and it 

 has been repeated elsewhere before other scientific gatherings 

 on several occasions since. Furthermore, an abstract of the 

 part of it relating to what is now called the cyclic origin of 

 rock-salt was published in my Opening Address to the Edin- 

 burgh Geological Society on November 19, 1896,^ and again, 

 in another form, in "The Genesis of Scottish Minerals," 

 Proc. Roy. Phys. Soc, vol. xiv., under " Epigenic Minerals," 

 pp. 184, 185, just quoted. It is not, therefore, correct to 

 state that the cyclic origin of rock-salt had been overlooked 

 until 1901. 



Since the dates above mentioned, several important con- 

 tributions to the literature of the subject have appeared. 

 One set of these has been put forward by Professor Joly, 

 Trans. Roy. Dub. Soc, ser. 2, vol. vii.; Geol. Mag., dec. 4, viii. 

 pp. 344-350 ; and Chem. News, vol. Ixxxiii. In these papers 

 Professor Joly has made use of some arguments relating to 

 chloride of sodium in favour of his view that the Age of the 

 Earth is somewhere between 96 to 105 millions of years. 

 The other set of observations referred to is by Mr William 

 Ackroyd, F.I.C, Public Analyst for Halifax. In the original 

 form I understand that the first of these was read before the 

 Yorkshire Geological and Polytechnic Society at Leeds, on 

 the 25th April 1901. The paper specially referred to con- 

 tains a valuable mass of data bearing upon the subject under 

 notice ; it was published in the Chemical News for the 7th 

 June 1901 (vol. Ixxxiii., No. 2167, pp. 265-268). I can only 



1 See also Trafis. Geol. Soc. Glasgow, vol. xi. p. 85, read April 22, 1897, 

 published in 1898. 



