40 



A qualitative chemical examination shows that 

 the blue beds are limestones, all more or less 

 impure, and that the grey beds are much more 

 impure varieties of the same rock. The pro- 

 portion of magnesia present does not seem in 

 any case sufficient to constitute a dolomite, 

 although in the absence of a quantitative 

 examination the actual proportion of this base 

 present remains uncertain. 



A microscopic examination of a series of thin 

 sections of specimens of the various varieties of 

 the rock, shows that all stages of the continuous 

 transition from a limestone containing only a 

 few flakes of brown mica to a micaceous para- 

 gneiss (pflastergneiss) are represented. The 

 latter constitutes the hardest grey beds and 

 holds scarcely any calcite, but contains, on the 

 other hand, much biotite, in the form of indi- 

 viduals, which usually possess a somewhat 

 frayed outline and lie in a fine-grained base of 

 colourless untwinned grains, some of which are 

 quartz, but some, and perhaps the majority, 

 are probably orthoclase. Pyrrhotite also occcurs 

 scattered through the rock, but no trace of any 

 magnesia constituent, except the biotite, was 

 found in any of the slides, nor was any mica 

 but biotite present. In most of the sections 

 minute rutile crystals, identical with those so 

 commnoly found in clay slate, were found. 



The occurrence evidently represents a great 

 body of calcareous sediments, made up of an 

 alternation of beds which vary greatly in the 

 amount of impurity (silt or mud) which they 

 contain, and which, under the relatively slight 

 metamorphism which this portion of the area 

 has undergone, has suffered a diagenetic alter- 

 ation into the varieties of limestone and para- 

 gneiss above described. In the movements to 

 which the strata have been subjected, the purer 

 limestone beds, curiously enough, are seen to 

 have been less resistant than the more impure 

 gneissic beds, for they can be seen on the 

 weathered surface to have been torn apart, 

 while the gneissic beds flow in between the 



