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bearing dolerite containing augite with basal striation. A specimen 

 from the Kilsyth quarry is a sub-ophitic dolerite composed of plagioclase, 

 augite, hypersthene and ilmenite or magnetite. The hypersthene is 

 markedly pleochroic, gives straight extinction and weathers into a deep 

 green alteration product. We have already noted that oli vines, rich in 

 iron, weather to a deep green serpentine, whereas those poor in iron 

 weather to a light green. Precisely the same is true of the rhombic 

 pyroxenes. The strongly pleochroic hypersthene of the Kilsyth rock 

 gives rise to alteration-products much deeper in tint than the feebly 

 pleochroic bronzite of the Whin Sill. Specimens from Croy and Stirling 

 show the augite with striation parallel to the basal plane. It would be 

 interesting to know whether these rocks are contemporaneous with the 

 Whin Sill which they resemble in so many respects and also whether the 

 intrusive rocks of Fife, referred to by Dr. GEIKIE as occupying the same 

 relations to the Carboniferous strata, are similar in their petrographical 

 characters. In the West of Fife basaltic lavas and tuffs occur in the 

 Calciferous sandstone series and in the lower part of the Carboniferous 

 limestone. Various intrusive rocks also occur. In the east of Fife 

 interbedded volcanic rocks are rare ; the most striking feature of the 

 district being the occurrence of volcanic necks now filled with lavas and 

 fragmental rocks. 



A general examination of the plagioclase-augite rocks of the Firth of 

 Forth led Dr. GEIKIE to recognize three principal types : (1) the diabases 

 or granitoid type ; (2) the dolerites and (3) the basalts. The rocks referred 

 to as diabases are coarsely crystalline and not porphyritic ; they occur as 

 intrusive masses, sheets and bosses. The constituents are felspar, augite, 

 titaniferous iron ore and apatite. The felspar is generally kaolinised. 

 Binary Carlsbad twins are very common, and hence Dr. GEIKIE was led to 

 the conclusion that orthoclase is frequently present/ 1 ) The augite some- 

 ' times occurs in eight-sided prisms and sometimes as large irregular ophitic 

 masses. It is as a rule unaltered. Olivine has not been certainly recog- 

 nized in these rocks. Apatite sometimes occurs in stout dusty prisms and 

 sometimes as minute colourless needles. Calcite, prehnite, pectolite and 

 analcime are known as minerals in these rocks. Pyrite is generally present. 

 Chalcedony and quartz also occur. Illustrations of this type may be seen 

 in Lindsay's Crag, near Kirkliston, at Crossal Hill, near Dalmeny ; at 

 Muchraw, near Torphichen, at Auchensteary, near Kilsyth, and at Croy and 

 the Carron Water above Denny. 



Rocks of the above type shade into the dolerites. These latter rocks 

 are markedly crystalline, except at the edges, where they become compact. 

 They are uniform in texture, and seldom become porphyritic or amyg- 

 daloidal. In some cases they are holocrystalline ; in others they contain a 

 certain amount of glassy interstitial matter They consist of plagioclase, 

 augite, titaniferous iron ore and apatite. Olivine is rarely present, and in 



(1) The felspar of these rocks is often pink. Hence, in hand specimens they remind one 

 of syenite rather than diabase. If the felspar consists of orthoclase to any considerable extent 

 they might be termed augite-syenites, 



