ON THE CRYSTALLINE ROCKS OP ANGLESEY. Ill 



of importance. While this is proceeding, Mr. J. 0. Hughes wili devote 

 nearly all his available time to such analyses as are likely to throw light 

 upon the origin of widespread types of rock in which metamorphism has 

 produced such complete reconstruction as to efface all traces of original 

 sedimentary or igneous structures. 



Of these rocks two have been attacked during the year now past, with 

 the following results: — 



No. 519a. — Great Jasper, Newborough. 



I. II. 



SiO a 93'51 93-54 



Fe 2 3 6'60 6'52 



Alkalies none -— 



100-11 100-06 



This is an unusually large jasper, occurring in a limestone associated 

 with the ellipsoidal diabase lavas. 



No. 231a. — Basic Schist, Capel Soar, Bodorgan. 



I. II. 



Si0 2 45-83 46-06 



Ti0. 2 trace — 



A1 2 3 17-45 17-34 



Fe 2 3 . u . 4-64 4-73 



FeO 7-52 7-46 



MnO trace — 



CaO 11-14 10-96 



MgO 8-37 8-21 



K 2 0-16 012 



Na 2 2-88 284 



H 2 (at 110°) 0-21 0-28 



H 2 (above 110°) 2-23 2-20] 



100-43 100-20 



This is a rock, now completely reconstructed, which is certainly 

 derived from the same lavas in another district. 



Besides these the following miscellaneous rocks have been analysed 

 on account of their special interest : — 



No. 426a. — Ophicalcite; Holyhead Island. — This is the beautiful 

 ' Mona marble,' associated with the Serpentines and Gabbros : — 



I. II. 



Residues insoluble in HC1 16-35 18-29 



Soluble Si0. 2 0-60 0-41 



Al 2 3 +Fe 2 s 9-17 8-31 



CaO 38-88 38-78 



MgO 2-44 1-98 



C0 2 31-08 3112 



H 2 undetermined — — - 



98-52 98-89 



As the above analyses indicate, digestion with hot HC1 is not very 

 suitable in this case. The rock evidently contains silicates which are 



