Vol. 59 .] 



THE TIKEE AJSD I0NA MARBLES. 



93 



If. General Description. 



The exposures of marble and gneiss near Balephetrish are shown 

 in the accompanying maps (figs. 1 & 2). Unfortunately, the relations 

 are much obscured by more recent deposits. It is clear, however, 

 that the gneiss has a general south-westerly and north-easterly trend, 

 and that the masses of limestone occur as lenticles of various si/.e 

 in the gneiss, exhibiting a similar foliation. The latter in the gneiss 

 is more or less interrupted by the large limestone-augen round which 

 it sweeps, and the result is great local irregularity in its direction ■ 

 the foliation of gneiss and limestone is, however, always parallel. 



Fig. 2. — Enlargement of a portion of fig. 1- 



On the shore west of Balephetrish the two rocks are most inti- 

 mately associated, some quite small inclusions and narrow streaks 

 of marble, besides larger masses, occurring in the gneiss. 



The marble is by no means of uniform character ; it will be 

 simplest to give brief descriptions of the main types noticed. 



(1) Pink marble of Balephetrish Quarry. — This is the 

 well-known Tiree Marble, so common in collections. The rock 

 consists of minutely granular calcite, with some subordinate 

 dolomite ; embedded in this compact carbonate-matrix are abundant 

 crystals of dark-green hornblende (often idiomorphic), and coccolite, 

 with scarcer greenish-brown mica, and minute brilliant grains of 

 pale hair-brown sphene. In other specimens coccolite is the 

 predominant or only silicate. Minute crystals of scapolite were 

 also found (in residues) by the late Prof. Heddle. 



