414 



Remarks on the 



[June, 



26. An Attempt to explain a Difficulty in the Theory of Vision, depending 

 on the ciitferent Refrangibility of Light. Phil. Trans. 1789, vol. Ixxix. p. 256. 



27. Observations of the Comet of 1793. Phil. Trans, 1793, vol. Ixxxiii. 

 ^. 55. 



•28. An Account of an Appearance of Light, like a Star, seen lately in the 

 dark Part of the Moon by Thomas Stretton in St. John's-square, Cicrkenwell j 

 with Remarks on this Observation and Mr. Wilkins's. Phil. Trans. 1794, voU 

 Ixxxiv. p. 435, 



Article II. 



Remarks on the Transition Rocks of Werner. By Thomas 

 Allan, Esq. F.R.S.E. Read to the Royal Society of Edin- 

 burgh in 1812. 



Although we have many writers on geological suhjectSj 

 whose works are distinguished by ingenuity of doctrine, and 

 novelty of opinion, and, among them, some who have made 

 advances towards arrangement, it was reserved to the celebrated 

 Werner to introduce means, by which rocks might be described 

 with some degree of precision. Many ingenious theories were 

 invented, to account for their formation ; but little or no atten- 

 tion was paid to the acquirement of an accurate knowledge, 

 either of their composition, or their relative position in nature; 

 although these certainly appear to be the bases, on which such 

 speculative opinions ought to be founded. 



But while we acknowledge these obligations to the Professor 

 of Freyberg, we cannot extend our unqualified approbation to 

 the systematic arrangement he has introduced. It was not to be 

 expected, that the labours of one individual, who, from peculiar 

 circumstances, was confined within certain limits,* were suffi- 

 cient to attain perfection ; nor could it reasonably be supposed^^ 

 that any district, however extensive, should be so singularly 

 favoured, as to contain all the variety of facts, that occur in 

 other parts of the world, from which deductions are to be drawn, 

 and elucidations afforded, investing phenomena with characters 

 which they do not present elsewhere. 



In forming his arrangement, Werner may have exhausted the 

 means he possessed ; he therefore ought not to be reproached,, 

 for although his conclusions are more general than are warranted 

 by the circumscribed field to which he was confined, yet he has 

 formed a ground work on which the labours of future geologists 

 may rear a system more capable of affording satisfaction. 



* In Werner's preface to his Theory of Veins, he states, that bis limited 

 fortune, and the nature of his present situation, prevented him from travelling 

 into more distant countries. Anderson's Translation, xxiii. 



