ISLA. GEOLOGY. 249 



which it follows. This limestone is exceedingly compact 

 and of a fine grain, like the primary limestones of many 

 parts of Scotland. It is not interlaminated with the 

 quartz rock, as those which lie in the schists are with 

 their accompanying rocks, but is often highly siliceous 

 in composition, and much indurated at the points of 

 contact with that substance. It varies from a greyish 

 to an ochrey white. These are the only limestones 

 which I observed in their places, arid I am unable to 

 give any more satisfactory account of their connexions 

 than that which may be drawn from the above state- 

 ments. Loose specimens of another limestone remarkable 

 for its cavernous granular texture are here found on the 

 surface, but whether only an accidental substance, or 

 portions of some bed, there were no means of knowing. 



The next rock remaining undescribed is a conglomerate 

 of a remarkable texture. The most accessible points of 

 observation are at Portaskeg, and at Lossit hill. The 

 rock at Portaskeg extends along the shore from Ardnahu 

 bay to within half a mile of the farm of Lossit, and may 

 also be traced inland ; but its relation to the limestone 

 is obscured in the interior by the soil, while, on the sea 

 shore, as was just shown, that rock does not occur. It 

 is in contact with the quartz of Ru vail on one side, and 

 is succeeded, at the short interval just noticed, by that of 

 Macarthur's head. In external general appearance, natu- 

 ral fracture, and the position of its masses, it resembles mi- 

 caceous schist so exactly that it might readily be passed 

 over as an ordinary bed of this rock alternating with the 

 quartz rock. In position it corresponds with that rock 

 on each side, the elevation of that which forms Macarthur's 

 head being about 45 and, on the other boundary, not 

 very different. In respect to composition it is a mica- 

 ceous schist, containing imbedded fragments of granite 

 and quartz rock of variable magnitude; and it may 

 with propriety be called a primary conglomerate. 



