J. W. Judd — On Volcanos. 245 



anterior and posterior faces of C. semicircularis " are nearly of equal 

 height, the anterior sometimes showing a basal ridge as in Petalodus." 1 

 In P. lobatus, on the contrary, the imbricating ridges on the posterior 

 face are much lower than those on the anterior. 



Locality. — Old Quarry on Crosshouse Farm, near East Kilbride, 

 from shale above the main Limestone, Lower Carboniferous Lime- 

 stone Group. In the cabinet of, and collected by Mr. James Bennie. 



EXPLANATION OF PLATE VIII. 



Fig. 1. Modiola Uthodomoides, R. Eth., Jun., Longnor, Derbyshire ; nat. size. Coll. 



Museum Pract. Geol. 

 Fig. 2. Modiola Uthodomoides, R. Eth., Jun., Beith, Ayrshire ; nat. size. Coll. Edinb. 



Geol. Soc. 

 Fig. 3. Petalorhynchus ? Benniei, R. Eth., Jun., Shiells Quarry, near East Kilbride; 



view of posterior face, x 2. 

 Fig. 4. Petalorhynchus ? Benniei, R. Eth., Jun., Shiells Quarry, near East Kilbride ; 



view of anterior face, x 2. 

 Fig. 5. Petalodus ? lobatus. R. Eth., Jun., Crosshouse, near East Kilbride ; view of 



anterior face, x 4. 

 Fig. 6. Petalodus? lobatus, R. Eth., Jun., Crosshouse, near East Kilbride ; view of 



posterior face, x 4. 

 Correction. — In my " Notes on Carboniferous Lamellibranchiata" (Geol. Mag. 

 1874, Dec. II. Vol. I.) an error occurs in the description of Plate XIII. (pp. 305-6). 

 For " slightly enlarged," and " natural size," read, all figures enlarged twice the 

 natural size. 



II. CONTEIBTJTIONS TO THE StTJDT OF VoLCANOS. 



By J. W. Judd, F.G.S. 



(Continued from page 214.) 



The Island op Isohia. 



PEEHAPS no district of equal area could be named in which so 

 many instructive illustrations of volcanic action may be wit- 

 nessed as the beautiful island of Ischia. Although only about six 

 miles long by four broad, yet this island exhibits a great central 

 volcanic mountain, — named "Epomeo" — surrounded by numerous 

 parasitical cones and craters, which, alike in their features and 

 their products, present the most interesting variations. 



After the well-known descriptions which have been given of the 

 island by Sir William Hamiltou, Scrope, Daubeny, James D. Forbes. 

 Scacchi, and many other observers, and the more complete treatises 

 of Signor Ferdinando Fonseca and Herr C. W. C Fuchs, dealing 

 respectively with its palaxmtological and petrological features, any 

 further account of its geology may seem to be unnecessary. But 

 a study of the physical features presented by the island, aided by 

 the light thrown upon them by the numerous valuable researches 

 above alluded to, appears to me to lead to a more complete reali- 

 zation of the nature, mode of action, and succession of the forces 

 to which the production of those features was due, than has as yet 

 been published, and enables us to reconstruct, in a more complete 

 manner than has been hitherto attempted, the geological history of 

 the island. In the following descriptions, therefore, I shall pursue 

 the chronological method, and, beginning with the oldest formations, 

 gradually pass to those of more recent date, until we at last reach 

 those the production of which is noticed in historical records. 



1 I.e. p. 73. 



