210 NOTES ON THE ANALYSIS 



pendicular, and the great folds may be traced all over the 

 country wherever exposures occur. 



Another important metamorphosing influence was the 

 intrusion of great masses of granite in Devonian time. The 

 effect of this was to harden the slate by baking it and to 

 produce many minerals which give a characteristic spotted 

 appearance as the contact with the granite is approached. 



It is this hardened slate from near the contact which 

 has received the name of iron-stone, and which is used for 

 building purposes. Microscopic examinations of a series 

 of sections of the slate taken from the proximity of the granite 

 contact made last year by Prof. D. S. Macintosh, gave 

 evidence that the folding took place prior to the intrusion 

 and also showed the development of a series of minerals, 

 such as cordierite, in small ovoid patches found even at 

 considerable distance from the contact, slender crystals of 

 anddiisite found nearer and also several other less prominent 

 minerals, such as biotite, sericite and muscovite. The small 

 amount of carbonaceous material in the orginal shale was 

 changed to graphite and feldspar and quartz particles are 

 found. Up to ihe present no fossils have been discovered, 

 a circumstance which points alike to its great age and the 

 severe metamorphosis that it has undergone. 



As found in most localities^ it is a hard dark grey rock, 

 characterized by red stains of ferric oxide where it has been 

 exposed to the action of the weather, of a rather homogeneous 

 structure and stony appearance. Bands are found which 

 contain so much silica and are so hard that they exhibit 

 the pher.omenon of conchoidal fracture. As the granite 

 contact is approached the slate changes its appearance slightly 

 and becomes what is known as spotted slate due to the de- 

 velopment of minerals. Patches and small crystals of pyrites 

 are common and under the influence of the weather, some 

 of the minerals have dissolved out, giving a pitted surface. 



