272 DE. A. GLLLIGAN OX THE PETBOGEAPHY OF [vol. lxXV, 



At a later date he writes : — 



' Since I wrote to you about uionazite I have looked into the matter a little 

 farther, and have now made separations from 52 granites and have recorded 

 the presence of monazite in 43 — a very high proportion, as you see. It is 

 less frequently present in the hornblende and sphene-bearing granites 

 than in the simple biotite-granites or the muscovite-biotite granites ; though 

 it is not absolutely absent from the sphene -granites, it is certainly much 

 rarer in these.' 



I have practically nothing to add to these remarks of Dr. Mackie, 

 except to point out that the granites which he found richest in 

 monazite are precisely the types found in the Millstone Grit. 

 Sphene I have not so far recorded : consequently, it would appear 

 that sphene-bearing granites were not abundant in the area from 

 which the material came. 



V. Heavy Mtneeals in Pebbles found in the 

 Millstone Geit. 



Some of the pebbles of granite and schist were large enough to 

 enable me to use a small portion for the separation of the heavy 

 minerals without destroying the whole pebble, which would be 

 most undesirable. The portion which was available for such work 

 was, however, too small to yield results that may be regarded as 

 satisfactory, and the list is only given for what it is worth. 



Perhaps the most remarkable result yielded by this part of 

 the work is the abundance of rutile, zircon, and tourmaline in 

 all the pebbles, whether granites or schists. Indeed, it will be 

 seen that tourmaline is most abundant in the schists. Monazite 

 is of somewhat rare occurrence, but that it should be found 

 at all is a remarkable fact. Apatite is also recorded from three 

 of the granites, while so far it has not been detected in any of 

 the separations from the grit. This mineral is generally regarded 

 as less liable to alteration than monazite, and is of common 

 occurrence in sedimentary deposits generally, so that its absence 

 from the grit is all the more remarkable. It must be noted, 

 however, that apatite-needles have occasionally been observed in 

 the quartz of the grit. 



Description of Minerals. 



Garnets. — These frequently show good crystal outline, but 

 are more usually in a fragmentary condition. In a few cases 

 they show the dodecahedral cleavage, and also contain inclusions ; 

 but all features due to alteration are, of course, absent. 



Iron Pyrites. — This only occurs in one of the schists, and is 

 in the cubical form, often as aggregates of small cubes. 



Magnetite. — This mineral is also of rare occurrence, and does 

 not show good crystal outline. 



Anatase. — As in the case of the anatase in the grit, it is 

 present most cominonry as a derivative from leucoxene, and occurs 

 as an outgrowth. A few good crystals have, however, been 

 observed, and are of the tubular form with low pyramids. 



