ON THE CRYSTALLINE ROCKS OF ANGLESEY. 321 
Of these No. 224 is one of the jaspers described in a paper by the 
Secretary. It will be seen that this is wholly unlike any igneous rock, 
being essentially composed of silica, with a little impurity, chiefly iron 
oxide. 
The analysis of a fine red phyllite associated with this rock is nearly 
completed. 
No, 224a, 
18 V.W. In Limestone 900 feet S.W. of Hendrebach. 
iT; II. 
SiO Rumreese ics 97/30 97-02 
ANG as Lente aay 0:30 
FesOgahtens eo ee. G4 1:78 
99:28 99°10 
Alkalies were estimated but not separated :— 
K,0 + Na,O between 0:56 and 0°46 
No. 3124 is one of the pink limestones associated with the jaspers. 
It is a true dolomite, but interesting from an unusual quantity of 
manganese, of which we hope to give a definite estimate next year. 
This, and not iron, is evidently the colouring matter, giving the peculiar 
delicate tint of rose. It occurs in the carbonates, which must therefore 
approach a little to Rhodocrosite. 
No, 3124. By Mr. Wm. Roszrrs, B.S¢. 
Lianddnyn Island, Breakwater Cove. 
IL. Il. 
Residues insoluble in 20 per cent. HCl. 5°80 5:87 
Fe,0, + Al,O, . : i : : =) 92300 2°75 
CaO : : . ; : i . 29°89 29°97 
MgO : : : : . . 18-63 18-89 
Co, : : 5 c 4 : . 42°80 42°88 
.. percentage CaCO, = 53°37 53°51 
- MgCO, = 38:92 39°46 
The proportion in true dolomite would be :— 
CaCO, : MgCO,=64:35 : 45-65, 
No. 242a is a dark schist which gives a black streak. It occurs in 
the mica schist zone of the central district. Rutile is abundant. The 
presence of graphite has been determined qualitatively, and two 
estimates also made ; but as Mr. Hughes wishes to revise these, the final 
result is held over until next year. 
No. 2704, also from the mica schist zone, has been examined on account 
of the abundance of Rutile. 
No. 270a. 
13.S.W. Bwloh y Fen. 500 fect S.W. MP. Holyhead 14. 
SiO, = 42-94 
TiO, = 2°54 
' Quart. Journ. Geol. Soc., 1902, p. 425. 
1907. Y 
