ASSOCIATED IGNEOUS ROCKS OE THE. AYRSHIRE COAST. 783 



be intrusive in the serpentine. They occur near the side of a burn, 

 which runs into the sea rather less than 100 yards north of the 

 toll-gate. I observed two to south and one to north. They are 

 veins rather than dykes. In the thicker parts they resemble dole- 

 rites, mottled dull white and dark grey (something like a fine variety 

 of the Corstorphine rock), and they appear to pass (debris and weed 

 made it a little difficult to trace the connexion perfectly) into thin 

 veins (less than 1 foot thick) of a compact pinkish grey rock with 

 dull green spots. 



I have examined one specimen of the coarser rock from the north, 

 and four of various degrees of coarseness from the south of the burn, 

 The result of this examination confirms my view of the igneous 

 character of these rocks. The coarser varieties consist mainly of 

 felspar (or rather of what was once felspar, probably plagioclase, but 

 is now an aggregate of earthy dust and bright-coloured irregular 

 microliths), of well-preserved augite, of a serpentinous mineral, and 

 of decomposed ilmenite. The finer variety is so completely decom- 

 posed as to show little of its original constitution. The slide is 

 rendered almost opaque by a brown dust, with occasional clear 

 interspaces, sometimes evidently pseudomorphs after a crystal, filled 

 with a serpentinous mineral. There is, however, no reason why 

 these may not once have been basalts, and more compact conditions of 

 the other rock ; for the original structure is quite as much oblite- 

 rated in a specimen of " white trap " from the coast near St. Monace 

 (Fife) in my collection. We have here, then, some doleritic dykes 

 intrusive in the serpentine. 



On ascertaining that some of the rocks included in the serpentine 

 in this neighbourhood were also doleritic, I was naturally struck by 

 the singularity of the occurrence of two dolerites in the same 

 locality with a serpentine of intermediate age ; and I have carefully 

 considered the point, as to whether the former set may not also 

 have been intrusive in the serpentine. Though I cannot say that 

 in one or two cases out of so many the relative ages of the supposed 

 " diorites " and the serpentine may not have been unnoticed by me 

 (as I was mainly occupied in investigating the question of their 

 asserted passage one into another), still I do not think it probable ; 

 and I feel certain that, as a whole, Dr. Geikie's " dioritic series " is 

 of earlier date than the serpentine, and that some at least of my 

 specimens came from rocks belonging to that series. 



Conclusion. 



It results, then, that after consideration of both the appearance in 

 the field and the results of microscopic examination, I see no escape 

 from the following conclusions : — 



1. That the serpentine of this district is intrusive, and, like so 

 many others, is an altered olivine rock. 



2. That there is no hypersthene rock, but gabbros of two ages, 

 both of igneous origin, the first extraordinarily rich in diallage, so 



