Miss Mary Johnsfon — A Jurassic Ganoid Fish. 309 



The latter mineral is never found in this particular type of rock save 

 at the extreme margin. 



Irregular grains of quartz occur abundantly in the micropegmatite, 

 even where it is freshest. This fact may be regarded as a presumption 

 of primary origin. Considering how prone the micropegmatite is to 

 decomposition, where it has formed the channels for the percolation of 

 weathering agents and for the solutions depositing secondary sub- 

 stances, one would expect that the quartz, if secondary, would appear 

 only where the micropegmatite is decomposed. The presumption of 

 primary origin is strengthened by the occurrence in the quartz of 

 projections and isolated fragments of micropegmatite, apatite, and 

 granules of augite. This is specially well seen in the coarse pink 

 rocks from Dumback and Fankerton quarries. 



EXPLANATION OF TLATE XII. 



Fig. 1. Granophyric Diabase, normal variety, Colzium Quarry. Ord. light; x 20. 

 The upper half of the field shows a large turbid area of micropegmatite enclosing- 

 idiomorphic crystals of plagioclase and augite. The lower half shows a large 

 plate of augite ophitically enclosing felspars. The clear space at the top 

 left-hand is a want in the slide. The black areas are skeletal ilmenite. This 

 slide represents the type that makes up the great mass of the sills and dykes. 



Fig. 2. Granophyric Diabase, coarse var., Croy. Ord. light; x 7. Mostly 

 plagioclase, micropegmatite, and ilmenite. Augite altered to serpeutiuous 

 products. This sUde shows the regular arrangement of the plates of ilmenite. 



Fig. 3. Granophyric Diabase, coarse var., Dullatur. Ord. light; x 10. This 

 slide also shows idiomorphic plagioclase and skeletal ilmenite embedded in a 

 turbid micropegmatite ground-mass. The augite is altered to serpentinous 

 products which do not appear very well in the photograph. The parallel 

 arrangement of the ilmenite is well shown here also. 



Fig. 4. Granophyric Diabase, Fankerton Quarry, near Denny. Ord. light ; x 20. 

 Felspar and augite in a turbid ground-mass of micropegmatite, which in places 

 (left-centre of tield) passes into clear areas of quartz. In the centre of the field 

 the micropegmatite is composed of minute rods arranged perpendicularly to the 

 idiomorpliic felspar. 



Fig. 5. Granophyric Diabase, Muchraw, Linlithgowshire. Ord. light ; x 10. 

 Clear felspar laths, curved blady augite crystals with ' herring-bone ' structure 

 accentuated by alteration, skeletal ilmenite and faintly turbid areas of micro- 

 pegmatite (top of slide). 



Fig. 6. Granophyric Diabase, Fankerton Quarry, Denny. Ord. light ; x 20. 

 Augite, turbid felspar, and still more turbid micropegmatite passing at the 

 bottom of the photograph into a large area of quartz. All constituents enclose 

 a great number of needles of apatite. The quartz encloses these and also isolated 

 areas of micropegmatite, and is undoubtedly original. 

 I am indebted for these photographs to Mr. Samuel Fingland, the University 



photographer, Glasgow University. 



[To he concluded in our next.) 



III. — On a New Specimen of the Jurassic Ganoid Fish, Pleuropholis 



L^EVissniA, Egekton. 



By Miss Mary S. Johnston. 



(PLATE XIII.) 



HAVING in a collection of fossils from the Lithographic Stone of 

 Bavaria a Ganoid fish, I consulted Dr. Smith Woodward, and 

 through liis kind assistance have proved it to belong to the rare species 

 Pleuropholis Icevissima. The species has hitherto been imperfectly 

 known, the only figure being by Egerton of a comparatively small 



