FELSPATHIC ROCKS. 39 



the lines which bound them also, never contain any matter 

 differing from the tabular masses. In the stratified structure 

 there is nothing precisely similar to this, and little that is 

 analogous. True stratified masses preserve a general line 

 of direction through a great extent, and if this is changed 

 or obliterated, it may be referred to the action of disturb- 

 ing agents. The lines of stratification are also generally 

 produced, by the rock becoming less compact in its struc- 

 ture, or by the presence of a minute layer of argillaceous 

 matter ; the bounding lines of tabular concretions are, how- 

 ever, only lines of division. Of the felspar class there are 

 three rocks, which may be considered as the most marked 

 individuals of this series. 



Compact Felspar, which is one of these, occurs of va- 

 rious shades of white, red, and grey, and by acquiring crys- 

 tals of felspar, it becomes Compact Felspar Porphyry. This 

 rock occurs in great abundance in the different felspar dis- 

 tricts, and forms hills both in the Garleton and Pentland 

 ranges. In size, the imbedded crystals of felspar vary from 

 the smallest size to near an inch, and are sometimes accom- 

 panied with particles of quartz and scales of mica. Clay- 

 stone, which is another member of this extensive class, is of 

 the same general colours as compact felspar ; in some in- 

 stances, the various shades of colour producing a veined or 

 mottled aspect; and as compact felspar, it occurs porphyri tic. 

 Of this rock the Lothians afford many examples; itismetwith 

 abundantly both in the Pentland and Garleton Hills. The 

 only other rock which presents characters sufficiently well 

 defined to justify its being considered as a marked variety of 

 felspar, is Clinkstone. This rock occurs of various shades 

 of bluish, yellowish, and greenish grey, and is often highly 

 impregnated with iron ; the presence of which causes 

 it to assume various modes of marking. It has frequent- 



