372 SKY. GEOLOGY. OVERLYING ROCKS. 



Two other varieties of this rock occur here, which 

 may be mentioned, although possessing no peculiar interest. 

 In the one, chlorite forms a constituent part, and in 

 the other a greenish compact steatite is intermixed with 

 the felspar and hornblende, the total compound being 

 not much unlike the porcelain granite of Cornwall. 



It is unnecessary to enter into a minute description 

 of the substances that are connected with the syenite by 

 transition. The general characters of these rocks are well 



proved by the observations of Mr. Von Buch in Norway, who has 

 described granite lying on black conchiferous limestone. This granite is, 

 according to that author, connected with porphyry, and there is no 

 reason therefore to doubt that the instance quoted by him is analogous 

 to this; although he has not entered into a full examination of its con- 

 nexions. His overlying granite will therefore prove, like this, a mere 

 variety, in a geological view, of the syenite and porphyry formation ; 

 another proof, if such were wanting, of the necessity of great caution in 

 drawing geological inferences from the examination of mere specimens 

 of rocks, and of the absolute necessity of tracing the actual connexions 

 of all those rocks which are subject to similar variations of character. 



In the next place, this syenite may serve to prove, that in many other 

 cases, the granites, which we have been accustomed to consider as prior 

 in formation to the secondary strata, if not to the primary schists, may 

 be often posterior to both: the opportunities for ascertaining their rela- 

 tions being wanting; sometimes from the total absence of the secondary 

 rocks in the places where they occur, at others from the impossibility of 

 obtaining sufficient access to them to enable us to ascertain a point of 

 great delicacy and difficulty, and in a third case perhaps from the demo- 

 lition and disappearance of those portions which may have once been 

 overlying, and have, as being the most limited and the most feebly sup- 

 ported, been removed through a long course of time by the ordinary 

 causes of waste. 



It is objected to the well known arguments in favour of the igneous 

 origin of granite, that if it had been protruded from below in a state of 

 fusion it should have flowed over the superincumbent strata: and the non- 

 existence of this fact has been asserted. But the present case, as well 

 as that of Mr. Von Buch, are in reality examples of it, as far as this 

 argument is concerned. It is not necessary that it should always occur. 

 But I have no wish to enter the field of controversy. In the words of 

 Erasmus, " Adeo invisae mini sunt discordiae ut veritas etiam contentiosa 

 displiceat." 



