Remarks on Dr. Boases Primary Geology. 549 



" The primary rocks have been divided into stratified and unstra- 

 tified, the latter comprising the various granitic rocks, which gene- 

 rally occur in large insulated clusters, and have a compact and mas- 

 sive structure ; the former denoting those non-fossiliferous rocks 

 which surround, and are intimately connected with the granite, 

 and are commonly distinguished by a slaty or schistose structure. 



" It will be found, however, that this division is perfectly arbi- 

 trary : for both stratified and unstratified rocks are so intermixed in 

 their associations, that it is sometimes impossible to decide to which 

 of these classes a rock, under examination, belongs: in order there- 

 fore in some measure to avoid this confusion the primary rocks will, 

 in the following pages, be supposed to consist of granitic and schistose 

 groups ; only understanding, by this division, that in the one gra- 

 nites, and in the other slates predominate ; and it must not be for- 

 gotten that this is an artificial, not a natural arrangement, merely 

 to facilitate description. 



''The rocks which immediately surround the insulated masses and 

 ranges of granite, are very numerous; and although they are gene- 

 rally schistose, they are sometimes massive, and in their structure 

 very similar to the granitic. These circumstances, however, will 

 come under consideration hereafter ; at present our object is to obtain 

 a knowledge of the composition and internal appearance of the indi- 

 viduals of the schistose group. 



" In describing the various schistose groups, that of Cornwall will 

 in the first place demand our attention. It may be divided into 

 two series, the porphyritic and the calcareous ; the former including 

 those rocks which occur next the granite, and contain porphyries 

 and other granitic rocks in the form of regular beds or elvan- courses, 

 and which abound in veins of tin and copper ores ; the latter, 

 comprising those rocks which are more or less remote from the 

 granite, contain no elvans, but abound much more in greenstone, 

 especially its obscurer varieties, and in dark-coloured limestones, 

 sparingly metalliferous, containing no tin, but productive of lead and 

 antimony ; and lastly, possessing occasionally organic remains. 



" Most of the rocks of the calcareous series appear to be referrible 

 to the older portion of that class which is intermediate between the 

 primary and the secondary, commonly known by the name of Iran- 



