456 Dr. Mac Culloch on Quartz Rock, 



is the perfect crystalline texture of quartz any proof of a primitive 

 formation ; since the strata of Kirkaldy, which belong to the fioetz 

 and coal formation, contain beds of highly crystalline and translu- 

 cent quartz, alternating with coal and organic limestones. 



The mode in which the felspar exists in this rock proves also 

 its mechanical construction, and shews that it has very probably- 

 been derived from the wearing and deposition of antient granites, 

 by whatever means we may attempt to account for its present 

 highly compacted and often crystalline structure. 



Having thus, as I trust, clearly proved that the rock of Jura is 

 a recomposed rock, as far as regards its structure, and that it cannot 

 from its compound nature be properly entitled to the name of a 

 granular quartz, it is our business to consider its geological appear- 

 ances, and the probable nature of the process by which it acquired 

 its present disposition. 



Before examining this question, it is requisite to premise an ob- 

 servation of professor Jameson, whose accuracy is not doubted. 

 He remarks that the " Quartz rock rises at an angle of 45 degrees 

 from under the micaceous schistus." Here then we have a rock 

 formed of a mixed mechanical deposit, lying under a rock which 

 is held to be primitive, and the third in succession from the first and 

 fundamental of all rocks, granite. I did not observe this fact, but 

 have perfect reliance on his observations, because they coincide 

 with what I have myself observed in other places. Either then 

 this mechanical deposit must be considered as a primitive rock, or 

 micaceous schistus is a rock of more recent formation than it has 

 been generally esteemed. 



This latter supposition may perhaps admit of further proof, but 

 I cannot enter into it in this place. 



Leaving this additional difficulty out of discussion at present, it is 



