428 MR. G. BARROW ON THE MOINE GNEISSES [NOV. 1904* 



fracture is not so marked, contains less andalusite but far more 

 shimmer-aggregate material. The most micaceous part of the rock, 

 with numerous spots on the splitting surface, shows marked parallel 

 structure under the microscope, and is composed of abundant pale 

 biotite associated with quartz, a little felspar, and some andalusite. 

 The elongated micas sweep round small patches in which no parallel 

 structure is seen, and these are probably eyes of material that have 

 been indurated anterior ^o the main crystallization of the mass, 

 and have thus escaped crushing. 



Now, the rock so rich in andalusite is seen again close to the Main 

 Limestone, both at the head of the corrie about a mile to the north- 

 north-east of Auchallater, and 2 miles to the south-south-west, in 

 the corrie opposite Newbiggin. It is thus clear that there is not 

 much more rock present in the whole of the Black Schist than the 

 few bands above described, and it cannot have been much more 

 than 15 feet thick originally. This will be understood by following 

 up Glen-Callater Burn as far as the ford ; there, except the 

 granite, nothing is seen but the Felspar-Kock and the closely- 

 adjacent material, repeated incessantly by folding. A difficulty 

 arises from the different phases of metamorphism ; for, when the 

 material was considerably heated anterior to the main meta- 

 morphism and indurated so as to escape subsequent crushing, it is 

 found, in this area, finally to crystallize as an andalusite-hornfels; but 

 generally, if much crushed, it finally assumes the form of a kyanite- 

 schist. In both cases, it will be noted that it is a non-magnesian 

 silicate that is so abundantly developed in the highest band. In 

 some cases, the andalusite appears as a number of minute laths that 

 in their mode of occurrence simulate kyanite, and in other localities 

 are replaced by kyanite. This gradual diminution in the amount of 

 clastic chlorite present in the original shales has been noted over a 

 wide area, and suggests continuous deposition or an unbroken 

 sequence from the Little Limestone to the rock rich in kyanite or 

 andalusite next the Main Limestone. 



For the purpose of building up the sequence the most valuable 

 evidence, however, is obtained from the association of the Main 

 Limestone with the Calc-Flintas, or altered, parallel-banded, calcareous 

 shales. The accumulated experience of years of detailed mapping 

 makes it certain that in these two rocks we have a record of con- 

 tinuous deposition, or a portion of an original and unbroken sequence : 

 no other bed in the series can intervene between them, and in any 

 account of the succession they must always be taken together. 

 Again, experience has shown that, with very rare exceptions, the 

 calcareous shales always overlie or succeed the main bed of Lime- 

 stone. Now these Calc-Flintas occur in most of the broader valleys 

 over a very large area, especially where the beds between the 

 Qnartzite and the Main Limestone are wholly missing. It must be 

 remembered that in the former case it is not merely the original 

 thickness of the beds that is missing, but the great mass of rock 

 built up by their intense folding ; a large gap is consequently left 



