450 D. Balsillie— 



smaller idiomorphio pyroxenes. Ilnienite in skeletal plates is an 

 ingredient of early separation. 



The Lathones rock microscopically is a reticulum of plagioclase 

 felspars ranging as in the coarse variety of the Crossgates rock from 

 oligoclase to labradorite. Some of the latter are earlier than the 

 olivine, which the mass evidently contained, as pseudomorphs of 

 this mineral are often to be seen penetrated by square-ended laths 

 of labradorite. Pyroxene of a distinctly purplish hue with curious 

 pale green borders, or sometimes entirely green, is an essential 

 constituent, the mineral being ophitic towards much of the felspar 

 and showing in favourable sections the dispersion usual in the 

 olivine dolerites. Ilmenite, biotite, a little aegirine, and not 

 inconspicuous interstitial orthoclase also occur : there is, too, 

 another felspar of low refractive index, which being optically 

 positive is probably albite. 



The consolidation history of the Lathones rock has not been one 

 continuous process, but there has been a period of resorption, for 

 many of the felspars and pyroxenes show signs of corrosion and 

 subsequent accretion. Secondary (?) albite, analcite, occurring 

 primarily but also replacing orthoclase, and chlorite are distributed 

 throughout. Many portions of the mass are full of little cavities 

 bordered by orthoclase and filled with analcite and zeolites. Clearly 

 the rock has been the subject of much alteration and change, but 

 how much of this should be regarded as belonging to its initial 

 thermal history and how much entirely secondary the writer is not 

 prepared to say. The diabases of Crossgates, Radernie, and 

 Lathones, it may be repeated, are not like any of the other olivine- 

 bearing rocks of the district, and probably in respect of their more 

 distinctly alkaline character should be relegated to the essexites. 

 A more careful analysis of their characters is reserved to another 

 time.-*- 



(3) Spalefield and Kingash tyjoe. — The rock of Spalefield has 

 long been known to geologists from the careful description of it 

 given by Dr. Flett. Since that time the teschenites have been 

 found to have a wide distribution in Central Scotland and to be 

 remarkably uniform in their general mineralogical attributes. The 

 distinguishing characters of these rocks are their abundance of 

 analcite, their strongly dispersing purple pyroxene, and their 

 intensely coloured hornblende. In addition to these constituents 

 occur lime-soda felspar and accessory minerals, among which 

 apatite is conspicuous. No example of a teschenite that has been 

 observed by the writer could be described with confidence as being 

 anything but a highly altered rock. Analcitic replacement of 

 felspar has taken place on a great scale in these masses and, without 

 derogation of the doctrine of the primary nature of some of the 



^ Dr. Peach recently informed me that many years ago in a traverse of this 

 around with Sir Archibald Geikie, they noticed these curious rocks ; there is,, 

 however, no reference to them in the East Fife Memoir. 



