488 ME. H. W. MONCEXON OK THE STIRLING DOLEEITE. [Aug. 1 895, 



are numerous small vesicles filled with, calcite. I have two micro- 

 scope-sections from this rock, one cut through and at right angles 



Fig. 3. — Dolomitic limestone. 



X450. 



to the top, the other cut nearly parallel to the top 3*70 inches 

 below it. Under the microscope the following characteristics 

 appear : — 



(i) The top zone, 0*02 inch broad, is yellowish-green and grey 

 in colour. There is not the spherulitic structure of the 

 specimen from locality 2 (p. 485), though there seems to 

 be an approach to it in the aggregates of iron oxide which 

 give a speckled appearance to the groundmass. The felspars 

 are porphyritic, but small and greatly altered. 



(ii) A zone O10 inch thick, in which the groundmass is grey in 

 colour and very fine-grained. The porphyritic felspars are 

 long and thin ; a large one measures 0*02 x 0-003 inch ; many 

 of them are fairly parallel to the top of the igneous rock. 



(iii) A greenish-yellow band 0*15 inch thick, with brown blotches 

 and well-preserved felspars which are white, though yellow 

 colouring has occasionally invaded small cracks in them. 

 This yellow colour is, I should think, probably due to the 

 nearness of the specimen to the surface of the ground. 



(iv) A zone 0*22 inch thick, with a grey groundmass more clouded 

 than zone ii. iron oxide in minute specks, and porphyritic 

 felspars. 



