Trof. T. G. Bonney — On the Rauenthal Serpentine. 65 



Buvette a Pont Neuf), a moorland hill affords a few Devonian fossils 

 in a grit belonging- to the schists of Morlaix. Further along the 

 road occur schists of Ploagastel altered by granite (of Pompol). 

 A quarry on the west side of the road, about two miles from the 

 town, shows garnets and chloritoid in the altered schists. About 

 a mile further, in another quarry about 100 yards west of the road, 

 behind some houses (Le Fume?), the schists have become leptinolite. 

 The road-sections, a little beyond, of granite tongues running into 

 schists, are as fine as I ever saw. 



An afternoon excursion from Morlaix took us a circuit north of 

 the town. We passed on the right bank of the river singular bedded 

 rocks (Schists of Morlaix), with a granite dyke cutting them, and 

 made deviations to see the quarry of Kerscou and its wonderful 

 junction of granite and schist (a strip of black shale, 30 feet long 

 by 18 inches broad, is included as if torn off), and at a hamlet 

 called Ploujean a unique porphyry dyke. Thence regaining the 

 main N.N.E. road we passed in a valley a diabase dyke badly seen in 

 road-sections, followed by some conglomerates, and arrived at the 

 head of the estuary of the Dourdu, where, by walking half a mile 

 along the northern strand, we were to have seen a limestone conglo- 

 merate; but a tide of phenomenal height obstinately continued to 

 rise and entirely barred our progress. Quartz conglomerates were 

 again seen in the road along the slopes above, and about the 5 kil. 

 stone from Morlaix, in shallow quarries for road metal, the Gres a 

 Scolithes. Thence returning through St. Antoine, and driving east 

 for several miles, we traversed the whole basin of the Morlaix 

 schists, until we again encountered the Gres rising from under 

 them. In a shallow quarry in the midst of fields, and almost buried 

 from sight, we were shown the locality where a few rare fossils 

 have proved its Cambrian age. This ended the excursion. 



The guiding idea in its arrangement was to show first the com- 

 plete series of unaltered beds, and afterwards the modifications 

 which these rocks present around the invading masses of granite. 

 I cannot attempt to reproduce in any way the interesting discussions 

 on these phenomena which occurred between the distinguished 

 geologists of the party. From my own observations I come back 

 with the sti'engthened conviction that it was no causes of this kind 

 "which gave origin to the crystalline schists. 



I desire to take this opportunity of expressing my gratitude to the 

 members of the party, and especially to its President, Dr. Barrois, 

 both for the opportunity of joining the excursion, and for the parti- 

 cular kindness and attention bestowed on me at every possible 

 occasion. 



III. — Note on Specimens op the Rauenthal Serpentine. 



By Professor T. G. Bonnet, D.Sc, LL.D., F.E.S. 



N the very valuable work on "British Petrography" by my 

 friend Mr. J. J. H. Teall, now in process of publication, there 

 is a rather full notice of an interesting serpentine which occurs in 



DECADE III. — ^VOL. IV, — ^NO. II. - 5 



