388 Professor T. G. Bonneij — Eroded Hocks in Corsica. 



EXPLANATION OF PLATE XII. 



Fig. 1. — Phacops {Chasmops) conicophthalmus, Boeck. Head-shield. Slade Bedsy 



Upper Slade, Haverfordwest, x 1|. 

 ,, 2. — Phacops [Dahnanites) sovialis, Barr. Yar. Nearly complete individuaL 



Orthis argentea zone, Prendergast Laue, Haverfordwest. Nat. size. 

 ,, 3. — Phacops [Chasmops) macroiira, Sjogr. ? Portiou of pvgidium." Sholeshook 



Limestone, Sholeshook Railway Cutting, Haverfordwest. Nat. size. 

 ,, 4. — Phacops {Dabna»ites) a&. incertus, 1)051. Pygidium. Slade Beds, Upper 



Slade, Havei'fordwest. x 2^. 

 ,, 5. — Encrinnrus innltisegmentatHs, Portl. Pygidium. Slade Beds, Cuckoo 



Grove Lane, Haverfordwest, x 2,\. 



II. — Some Eroded Eocks in Corsica. 



By Professor T. G. Boxney, D.Sc, LL.D., F.R.S. 



(PLATE XIII.) 



A S I have recently seen certain cases of the curious hollowing 

 ]\_ out of rocks in Corsica, described by Mr. F. F. Tuckett (with 

 a note from myself) in the January number of this Magazine, for 

 which Mr. Lake suggested an explanation in the following number, 

 I will add something to that note and intimate why I did not 

 refer to desert regions for an explanation. The case which Mr. Lake 

 mentions ("Das Gesetz der Wiistenbildung," fig. 7) undoubtedly 

 much resembles Mr. Tuckett's photographs, and so, to some extent, 

 do figs. 16 and 17, more especially the latter. With these I was 

 not then acquainted, perhaps having overlooked the book, because 

 I wrote a notice of " Die Denudation in der Wiiste," when it 

 appeared in 1891, and had formed the opinion that the author 

 was disposed to work his hypothesis for rather more than it would 

 stand. As, however, I knew there would shortly be a chance of 

 my getting a glimpse of the Egyptian desert, I postponed stating 

 why I had not suggested that kind of atmospheric erosion. In this 

 region, however, 1 saw no more than I already knew, but on our 

 return, owing to an unexpected change of plans, we spent an 

 afternoon and part of the next day in harbour at Ajaccio, when, 

 by a lucky chance, I hit upon some curious instances of erosion, 

 which I think may be worth a brief description. 



After strolling through the town, I walked from the Place 

 Bonaparte to a quarry which has been opened at the foot of the 

 hills. These rise rather steeply from the town, and must be sloping 

 just at this point roughly to the south-east. The rock was a fairly 

 coarse porphj'ritic granite, grey with a tinge of pink, with the surface 

 but slightly decomposed.' I rambled up the slope, on which out- 

 crops of granite are often frequent, attracted by the beauty of the 

 wild-flowers, until I reached a road running along the hillside, 



1 A thin slice shows the rock to be, for a granite, in good preservation. Enough 

 to say that it consists (apart from minor details) of quartz, biotite, and felspars, 

 some of which (probably orthoclase) , by enclosing smaller crystals of another species 

 (usually a plagioclase), and by a peculiar mottling and streaking (perhaps a result of 

 strain), recall the felspars of one or two Alpine granites, such as the protogine of th& 

 Mont Blanc range or that on the upper part of the St. Gotthard Pass. 



