4^7 



ftrata are accumulated on one another, and very convenient for exami- 

 nation, all thefe perpendicular fiffures have efcaped me, though in his 

 own words, there is not in nature an appearance more dijiina. 



Dr. Hutton feems to have forgotten, that he had faid, (page 224,) 

 " it is neceffary to look into thefe confolidated maffes themfelves, 

 " in order to find principles from whence to judge of thofe operations, 

 " by which they had attained their hardnefs or confolidated ftate." 



And alfo, to have forgotten the rule he lays down, ("page 273)' 

 " that, in order to have demonftration in a cafe of phyfical inquiry, 

 " we muft have recourfe to the book of nature.'" 



Now, I conceive this book fliould be referred to, like other books, 

 by quoting chapter and page, and not by indefinite general affertion, 

 that it contains fuch and fuch proofs. 



I am aware, that Dr. Hutton confiders our whyn dykes as filling 

 up rents or fiffures in the flrata, occafioned by their contraftion in 

 cooling. 



I have fhewn in a preceding memoir, that it is by no means clear 

 thefe mighty walls are of pofterior formation to the ftrata they cut 

 vertically, and alfo admitting the chafms to be antecedent, that they 

 were not filled by glowing lava, as Dr. Hutton fuppofes ; at prefent, 

 we have only to enquire whether thefe immenfe fiffures were formed 

 by the contraftions of the ftrata in cooling, I fliall, therefore, ftate 

 fuch facts alone as feem to me applicable to this point. 



The diftance between our dykes feems too great to fufEce for the 

 contraftion of the ftrata ; at the Giant's Caufev/ay we have fix in the 

 fpace of a mile and half, at Fairhead. five in nearly the fame extent ; 

 the intervals between the dykes, in both places, are, by Dr. Hutton's 

 own account, too great; he obvioufly infinuates we fhould find the 

 Mures frequent, and pofitively afferts there is no confolidated flratura 

 that wants them, yet the greater part of our precipices have not any whyn 

 dykes, or fiffures j at Cave-Hill, near Belfaft, where the perpendicular fa- 



( 3 N 3 ) cade 



