BUTE. GEOLOGY. 457 



remarkable; all the grains being closely packed and 

 separated by the least possible quantity of the mica, 

 so as to give it an undulating appearance. In general, 

 the quartz is transparent and crystalline ; but in the 

 coarser varieties, it is not unusual to find some of the 

 grains consisting of a saccharine opake quartz; and in 

 these cases the specimens might easily be mistaken for 

 gneiss, as the latter present a resemblance to felspar 

 which can only be discovered to be fallacious by the 

 lens : the deception is particularly strong when, as is not 

 unusual, they have a pink hue. As real grains of felspar 

 do however occasionally occur, this variety must, in strict- 

 ness, be ranked with gneiss. 



The chlorite schist occurs under a much greater va- 

 riety of aspects. It presents among others a set of 

 varieties precisely similar to those just described ; chlorite 

 being substituted for mica.* It is also found in a more 

 ordinary form ; consisting of scaly chlorite interlaminated 

 with quartz, which is more or less continuous, or else 

 granular. In a simpler form, it consists of an intimate 

 and fissile mixture of quartzose sand and chlorite ; the 

 former becoming occasionally so fine that it cannot be 

 detected by the eye ; when the specimens assume a dry 

 earthy aspect. From this it passes gradually, either into 

 the common continuously laminar, or scaly variety of 

 chlorite schist; being either straight or undulated, and 

 often possessing a high degree of lustre. At this extre- 

 mity of the series it graduates into common clay slate ; 

 while, at the former, it is connected by a transition equally 

 undefineable, with micaceous schist. 



The clay slate presents, like the former substances, a 

 considerable diversity of character. Where it is imme- 

 diately united with the chlorite schist it is often greenish, 



* Among many varieties which it would here be superfluous to 

 describe, a remarkable one occurs containing green compact felspar 

 intermixed with the other ingredients ; which, rigidly considered, is 

 also a gneiss. 



