ASSOCIATED IGNEOUS ROCKS OF THE AYRSHIRE COAST. 773 



a felstone becomes a diorite "). That this is a dolerite there can, I 

 think, be no doubt. The structure is very characteristic ; the pla- 

 gioclase felspar, both in the large and small crystals, though often 

 rather altered, is clearly recognizable ; the augite is perfectly distinct. 

 There is an iron peroxide, probably ilmenite, a greenish serpentinous 

 pseudomorph probably replacing olivine, and perhaps a little apa- 

 tite*. 



(4) Specimen from a reddish variety, with porphyritic crystals of 

 white felspar, from road-cutting south of Carleton Port Point. 

 Though much iron-stained, I think there can be no doubt of the 

 doleritic character of this rock ; plagioclase and augite can still be 

 clearly recognized, though in parts both are more or less replaced by 

 secondary products. A vein of zeolite (? pectolite) crosses the slice. 



I also selected two specimens of a compact black rock represent- 

 ing another common variety. At that time, not having realized how 

 slight was the evidence of extreme metamorphism, I thought this 

 might be some kind of highly altered " mudstone," though in some 

 respects it much resembled a compact basalt. After microscopic 

 examination I have little doubt that it has been a basalt with a micro- 

 crystalline or perhaps glassy base. The structure of one is not very 

 distinct, as the specimen was taken from close to a junction with the 

 serpentine, and the exterior of the specimen has become of a greyish 

 colour (as is common with basalts) ; but still many small decomposed 

 plagioclase crystals, and a little minute augite, can be seen, and the 

 microscopic structure is far more like that of a "white trap" than 

 any sedimentary rock known to me. Before the blowpipe it fuses 

 easily to a black glass. The Other is a section of one of some curious 

 protuberances on the face of some of the rocks near Lendalfoot, at 

 first sight almost like an amygdaloid (except that it seems formed of 

 the rock itself, which resembles the last). This also can, I think, be 

 nothing but a glassy basalt. The usual pseudomorphs have replaced 

 the felspar, and the augite is rather altered, but a little is still fairly 

 characteristic. On the inner side of the slide the rock is more cry- 

 stalline. No doubt some of the rocks of the district are of sedimen- 

 tary origin ; but, as far as I remember, the majority of those near 

 Lendalfoot resemble the above. They accordingly do not favour the 

 idea of extreme metamorphism, and do not contain hornblende, but 

 augite ; hence the epithet dioritic is inapplicable. If, however, I am 

 able to revisit the district, I purpose to examine this series much 

 more in detail, in order to separate the igneous from the altered 

 rocks • for the latter are undoubtedly present. 



* Some of the larger felspar crystals contain numerous minnte microlitbs of 

 a resin-brown colour ; their forms seem to be a very short prism of hexagonal 

 or octagonal section, but this is commonly not well defined. In general form 

 they much resemble crystals of the first system ; but they are certainly doubly 

 refracting, and, I think, not uniaxial. The mineral appears to be the same that 

 I have observed in the felspar of other basalts (e. g. some of those from Arthur's 

 Seat), and is probably augite. Prof. Rosenbusch ('Mikroskop. Physiographic,' 

 vol. ii. p. 461) describes a mineral which appears to be similar to this, and thinks 

 it may be rutile. This, however, is, of course, uniaxial, 



