The Rev. D. "Williams 07i the Devonian System. 117 



as 6S096 Italian miles. He mentions besides a common mile 

 whicli he says is of 1000 common paces. But of these com- 

 mon paces, which are his own and those of all men of or- 

 dinary stature, he says that five make six geometrical paces. 

 His words are, "Horum autem passuum (qui mei et cujusque 

 hominis staturae mediocris sunt) quinque sex geometricos passus 

 efficiunt." Hence, according to him, the common pace is six 

 of his feet, or the simple step (half of the pace) is three feet. 

 Now if this foot were as long as the English foot, this gives 

 too much, for it is well known that the yard is a long and 

 forced step for a man of moderate stature, whose walking step 

 is rather under than over 30 inches; and Fernel says he walked 

 from the palace to St. Denis and found it 5950 commo7i paces, 

 and also the whole length of Paris, which he found 2110 

 paces. But to make 68,096 geometrical paces exceed 69 

 Eno-lish miles, his step must have exceeded an English yard 

 and 2\ inches. There is then this alternative : — if his walking 

 step, described by himself, was that of other men, his degree 

 is demonstrably four or five miles wrong; but if he would 

 have us believe that he walked, or rather strided, 5950 paces, 

 at the rate of 38| inches each step, or half-pace, he must have 

 been a deceiver, either of himself or others, to an extent which 

 makes his evidence incapable of being i-eceived. 



I remain. Gentlemen, yours faithfully. 

 University College, Jan. 1, 1842. A. De Morgan. 



XX. Plausible Reasons and positive Proofs, s/iotoing that 7io 

 Portion of the Devonian System can be of the age of the Old 

 Red Sa7idstone. By the Rev. D. Williams, A.M., F.G.S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



PROFESSOR Sedgwick and Mr. Murchison having re- 

 cently contended for the identity of the Old Red Sandstone 

 with the 'many varied rocks of the Devonian system, the 

 former in a late supplemental memoir to his " Synopsis of 

 stratified Rocks inferior to the Old Red Sandstone," and the 

 latter by using them as convertible terms in your Journal for 

 December last, 1 feel it a duty I owe to truth, to caution geo- 

 logists and your readers generally, that it is not the fact, and 

 never can reasonably be assumed to be so, without a viola- 

 tion of the only safe laws which govern observation and legiti- 

 mate induction. 



Professor Sedgwick draws his conclusion from the following 

 syllogism : — " Any formation with fossils intermediate between 

 the Carboniferous and Silurian systems, must have an inter- 

 mediate position, must therefore be on a parallel of some part 



