254 PKOF. T. Gr. BONNET ON HOENBLENDE-PICEITE 



18. Additional Note on Bottldebs of Hoenblende Piceite near the 

 Westeen Coast of Angleset. By T. G. Bonnet, M.A., F.K.S., 

 Sec. G.S., Professor of Geology in University College, London, 

 and Fellow of St. John's College, Cambridge. (Bead April 25, 



1883.) 



In a short communication printed in this Journal (vol. xxxvii. 

 p. 137) I described a large boulder of hornblende picrite which I 

 found near Pen-y-Carnisiog in the autumn of 1880. Last summer 

 I had an opportunity of spending an afternoon upon the western 

 coast of Anglesey, and made use of it to examine the interesting 

 section to the south of Porth Nobla. I did not, however, neglect to 

 look out for boulders, as I thought it not impossible that I might 

 meet with some more picrite. In this I succeeded beyond my 

 expectations, and now lay the results before the Society, together 

 with some remarks on the microscopic structure of the specimens 

 collected. 



After quitting the railway at Ty Croes Station, I walked a short 

 distance along the road to the south-west, and then turned up a 

 field-way leading past a small farm called Bryn Gwyn. A short 

 quarter of a mile from it a boulder (No. I.), perhaps roughly trimmed, 

 has been utilized as the capstone of a gate-post. It measures 2| x 2 

 X 1| feet*. A small fragment projected, which I was able to detach 

 for examination without injury to the stone. 



The next (No. II.) was a well-rounded boulder lying on the sandy 

 shore at Porth Nobla. This had a rather greener matrix than those 

 which I had previously seen : and the porphyritic hornblende or 

 augite crystals were not quite so large. It measured about 2 feet 

 each way, and rose about 1 foot above the sand. Near the shore, 

 in the little cove Pen-y-Cnwc, is a boulder measuring about 

 Ah X 3 X 2 feet (No. III.), and within a short distance a smaller one 

 about 2 feet in longest diameter. At the cromlech Barclodiad-y- 

 gawras, further south, two of the supporting stones on the western 

 side are, I have no doubt, picrite of the ordinary type ; but of course 

 I did not touch these with my hammer. Three others are dark 

 augitic (or hornblendic) gabbro-like rock, common in boulders in this 

 part of Anglesey. 



On my return from Langwyfen to Ty Croes, by Prondwl, I noticed 

 a small picrite boulder built into a wall by the road-side ; and then 

 (a little over a mile from the station, and perhaps 300 yards from 

 a chapel) I found no less than seven fragments of picrite, five of 

 them being built into a rough wall, and one lying on either side 

 of it (No. IV.) They ranged from about 2 to 4 feet in longest dia- 

 meter ; but the time at my disposal did not allow me to go into details. 

 I should suppose they were fragments of one boulder ; if so, it must 

 have been even larger than that which I saw at Pen-y-Carnisiog. 

 * Measurements throughout are only approximate. 



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