MULL. GEOLOGY. 56? 



no circumstance presented itself sufficiently rare or re- 

 markable to deserve notice.* The trap occupies the 

 whole land from the sea to the surface, and is disposed 

 universally in flat terraces. Columnar forms are not 

 uncommon, and they are varied by the usual disorderly 

 recurrence of greenstone, basalt, trap porphyry, amyg- 

 daloid, and trap conglomerate. Fine specimens of 

 analcime, as well as of mesotype and of stilbite, are 

 found in different places; together with red ferruginous 

 clay and occasional specimens of prehnite. 



The middle trap district lies in the divisions of To- 

 rosay and Gribon, and is incumbent on the primary 

 and secondary strata already described. It rises to 

 a great elevation, apparently not far short of 2000 

 feet, and, like the northern division, is also disposed 

 in terraces ; its broken western side exactly resembling 

 the western cliffs of Sky, and containing similar alter- 

 nations of the several substances found there. It is tra- 

 versed by great veins of basalt, which also cross the 

 strata beneath, and of which some are so remarkable 

 for their schistose structure that it is with difficulty 

 they are distinguished at first sight from beds of blue 

 slate. Columnar forms are not abundant among these 

 rocks, but some of a very remarkable character are to 

 be seen on the shores opposite to Loch Laigh. These 

 are for the most part curved and implicated in various 

 intricate directions, generally surrounding the openings 

 of two or three small caves that occur in these cliffs. 

 They pass gradually into the amorphous basalt which 

 constitutes the body of the hill. Among them are to 

 be found some groups of straight columns of a small 

 size, being from six to nine inches in diameter, and of 



* I shall not be surprised if hypersthene rock should be found in 

 this part of the island, and beg to point out the shore between Loch 

 Mingary and Bloody bay as requiring a more accurate examination 

 for this purpose than the weather allowed me to bestow on it. 



