ON THE GEOLOGY OF ARDROSSAN. 609 



IV. 



DESCRIPTION OF PLATE II. 



Fig. 1. Basalt, Harbourback. The tiny lath-shaped felspars are arranged in rude fluxion streams. The 

 lark-coloured minerals are aggregated into heaps, the augite being almost entirely decomposed and replaced 

 >y calcite and chlorite. x 20. 



Fig. 2. Olivine-basalt, Castlehill. The small phenocrysts of olivine are much serpentinised, and set in 

 i ground-mass of felspar microlites and augite and magnetite grains. x 20. 



Fig. 3. A much corroded xenocryst of quartz from the Inches basalt, with groups of oligoclase 

 microlites formed as the result of the acidification of the basic magma. x 20. 



Fig. 4. Hornblende dolerite, upper part of Castle Craigs. The small crystals of augite and hornblende 

 are more or less idiomorphic, the former much decomposed. The felspars are fairly fresh, and the interstices 

 are filled with analcime and calcite. x 40. 



Fig. 5. Hornblende picrite, Castle Craigs. Crystals of olivine and augite are enclosed in large plates 

 of hornblende. A little decomposed felspar appears in the upper part of the section. x 30. 



Fig. 6. Hornblende picrite, Castle Craigs. Olivine and hornblende are the principal constituents. 

 Irregular crystals of augite are enclosed in the hornblende, and a little cloudy felspar occurs interstitially. 

 x30. 



TRANS. ROY. SOC. EDIN., VOL. XLV. PART III. (NO. 22). 86 



