The Rev. D. Williams on the Cornish Killas 25 



Fernel respecting the length of the geometrical pace. His 

 words are, " Neque audiendus est Fernelius, qui lib. i. Cos- 

 motheoriae c. i. in Schol. ait passus 5 hominis mediocris sta- 

 turse efficere passus 6 geometricos, et parte 4 Praxis Geome- 

 tries pedem geometricum exponit qui ad Romanum Vespasi- 

 anicum est ut 1030 ad 1200." 



On the grounds above stated, — the total absence of direct 

 testimony that the line figured in the Monalosphcerium is a 

 copy of the foot used by Fernel, and the improbability of the 

 consequences resulting from the supposition, — I think we 

 must conclude either that the diagram was intended for nothing 

 more than to illustrate the description of the measuring rod, 

 or else that it was reduced by the printer; and that the ques- 

 tion as to the true length of Fernel's degree remains as doubt- 

 ful as ever. At the same time, considering the great uncer- 

 tainty in which every thing connected with Fernel's operation 

 is involved, and seeing that we have nothing better than con- 

 jectures to reason upon, I must own that it is with considerable 

 diffidence I give my opinion in opposition to that of Professor 

 De Morgan, who has evidently bestowed much attention on 

 the subject. 



I remain, Gentlemen, faithfully yours, 



May 12, 1842. T. Galloway. 



IV. Supplementary Notes on the true Position in the " Devonian 

 System " of the Cornish Killas. By the Rev. D. Williams. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 TN one of the earliest communications I had the honour of 

 ■*- submitting to the public through the medium of your va- 

 luable Journal, I pointed out both by text and section, that 

 the Cornish killas was the last or newest formation in " the 

 Devonian System." I entertained such entire confidence in 

 the Chudleigh Sections, as much from their own evidences 

 as from the crowd of contradictions and apparent anomalies 

 elsewhere which they reconciled, that I felt no hesitation in 

 committing myself absolutely to them, from the conviction 

 that (as Nature could not deny herself) I should meet with 

 nothing but additional confirmations in the large portion of 

 country which I had not then surveyed. A recent excursion 

 into Devon and Cornwall haying furnished me with some im- 

 portant structural facts in addition to those I communicated 

 in your Number for February last, I request permission to 

 detail them to your readers, some of whom, in whose conver- 

 sion I am more particularly interested, however silent, may 

 not yet be satisfied. 



