136 MR J. D. FALCONER ON THE 



masses, small ophitic plates, or tiny idiomorphic crystals between the felspars. Residual 

 glassy base may be present in small quantity as intersertal material, and sometimes 

 portions of the matrix are felspathic and replaced by analcite as described above. 

 The quarries at North and South Mains furnish good examples of this type. Somewhat 

 finer-grained varieties with a similar structure are common in the Bo'ness hills. (See 

 PL I. figs. 1, 2.) 



2. Fine-grained basaltic rocks, porphyritic with olivine and augite. The felspar of 

 the groundmass is more abundant than the augite, and owing to a slight increase in the 

 amount of glassy base assumes very generally a fluidal or parallel arrangement. The 

 small augites are idiomorphic or granulitised, and more or less aggregated between the 

 felspars. The lava of Duncanseat quarry may be taken as a typical example.* (See 

 PI. I. fig. 3.) 



3. Fine-grained and compact basaltic rocks, porphyritic with olivine and augite. The 

 augite and felspar of the groundmass are in approximately equal quantity, and homo- 

 geneously mixed with a little glassy base. Fluxion structures are typically absent. 

 The basalt above the limestone at the Knock shows this structure fairly well. (See 

 PL I. fig. 4.) 



4. Compact basaltic rocks, porphyritic with olivine and augite. The augite of the 

 groundmass is much more abundant than the felspar, and usually granulitised. The lath- 

 shaped felspars form an open network, the meshes of which are filled with heaps of 

 augite granules. A small quantity of glassy base is usually present. The basalt of 

 West Kirkton quarry is a typical example.! (See PL I. fig. 5.) 



5. Compact lustrous basalts, porphyritic with olivine and augite. Brown glassy base 

 is abundant, and the felspar of the groundmass is usually reduced in amount. When 

 the felspar is almost wanting, the rocks assume a limburgitic character. Good examples 

 of this type may be found in the quarries at Tartraven and Kipps. (See PL I. fig. 6.) 



The silica has been estimated in one example of each type with the following 

 results : — 





Type 



Type 



Type 



Type 



Type 





I. 



II. 



III. 



IV. 



V. 



Si0 2 



45-65 



44-41 



41-20 



41-53 



41-39 



I. Fine-grained dolerite, Bell's Knowe, Bo'ness. 



II. Basalt, north of Tartraven Castle. 



III. Basalt, 300 yards south of Kipps Hill. 



IV. Basalt, old quarry, 300 yards S.S.E. of Hilderston Hills. 

 V. Basalt, western slope of Cockleroy. 



Types I. and II., the more felspathic varieties, are, as was to be expected, somewhat 

 more acid than the others. Types III., IV., and V. have practically the same amount of 

 silica. The differences between them in mineral composition must therefore be due 

 largely to variations in the rate of consolidation. Only in the Riccarton Hills is it 



* A. Geikie, Trans. Roy. Hoc. Edin., vol. xxix., 1880, PI. XI. fig. 4. t Ibid., PI. XI. fig. 5. 



