102 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 11, 



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blackish hue. In the midst of this mass 

 of clay-slate there is a bed of Kmestone 

 (fig. 1 1) ; and both the limestone and 

 the slate beside it often contain a large 

 proportion of magnesia, and the vary- 

 ing metamorphism of these beds has 

 in some localities given rise to masses of 

 serpentine and taleose slate. This slaty 

 series is covered by a second or upper 

 group of arenaceous strata (fig. Ic), 

 often assuming the character of quartz- 

 rock of a very pure white colour, form- 

 ing the top of many of the hills of this 

 district. Although in many places this 

 upper quartz-rock is much worn away, 

 yet in some of the mountains in the 

 higher parts of the county it attains a 

 great thickness, and forms the upper- 

 most bed of the old metamorphic rocks 

 exposed in this region. 



"We see therefore that the arrange- 

 ment and succession of the metamor- 

 phic strata here are very similar to 

 what we find in Bute and Argyleshire 

 (see Quart. Journ. of Geol. Soc. 1860, 

 vol. xvii. p. 133), namely a mass of 

 clay-slate enclosed like a sandwich be- 

 tween two great masses of arenaceous 

 beds. The rocks of Banffshire, in fact, 

 seem to belong to the same formation 

 as those of Bute. That is to say, they 

 form the north-eastern extension of 

 those beds which range through the 

 central Highlands of Scotland, from 

 the Moray Firth to the Firth of Clyde. 

 In mineral quality and state of meta- 

 morphism the resemblance is very 

 close. 



1. TJie Lower Division, or Gneiss and 

 Quartz-rock. — The passage from the 

 lower quartz-rock upwards into the 

 slates may be clearly seen along the 

 course of a small stream, locally 

 known as the Burn of Mulben, on the 

 east side of the Spey, which is tra- 

 versed by the line of railway from 

 Keith to Elgin. Near the mouth of 

 the stream, where it falls into ihe 

 Spey, the mineral quality of the rock 

 is, when freshly broken, white and 



