TIREY. GEOLOGY. 5 1 



with a large irregular fracture, and showing greenish yel- 

 low stains in the natural rifts. This seems to arise 

 from an admixture of serpentine or steatite. The same 

 substance is found dispersed through it, either in 

 small lumps or in minute grains of a dark green or 

 yellowish hue; the specimens differing in 110 respect 

 from the well known pebbles of similar marble which 

 are found in lona. This variety is highly ornamental, 

 but there does not appear to be any extent of it 

 applicable to useful purposes. The variety which con- 

 tains sahlite seems to be considerably more abundant. 

 This mineral is dispersed in the form of small grains, like 

 the coccolite of the pink marble, through a pure white 

 calcareous ground, the crystals being in general thinly 

 disseminated, and of a pale, or light blueish, or dark 

 greenish grey colour. These grains are also at times 

 crowded together in detached lumps of the size of a nut, 

 and from that to the size of an orange, or larger. Where 

 the surfaces have been exposed to the weather they are 

 readily seen ; not so much by their own superior perma- 

 nence, as by that of a nodule of the marble immediately 

 surrounding them, which is always much tougher and 

 harder than the general body of the rock. 



The last calcareous rock which I observed in Tirey is in 

 Gott Bay. This is a blueish limestone containing much 

 mica, and of a very tough constitution. It forms a nearly 

 vertical set of irregular beds of no great extent, accom^- 

 panied by gneiss and traversed by granite veins; in 

 which latter circumstance it differs from the calcareous 

 rocks before described. These veins may be traced 

 passing from the gneiss into the limestone. The action 

 of the sea having deeply corroded the upper edges 

 of the beds, has brought to light an intricate con- 

 tortion which they seem to have undergone. This it 

 has effected by acting on the micaceous laminse, thus 

 separating the flexuose calcareous strata by deep erosions. 

 There is a great resemblance between the contortions of 



