348 J. W. Judd— On Volcanos. 



Prof. Hall has likewise described from the Guelph formation of 

 Wisconsin such well-known Niagara Gasteropods as Platyceras Nia- 

 garehsis, Hall, and Platyostoma Niagarensis, Hall. At Cedarville, 

 so far as my observation went, the Guelph Limestones are destitute 

 of Gasteropods ; but they occur elsewhere in the State of Ohio in 

 this deposit in considerable numbers. 



As regards the Cephalopoda, the Guelph Formation has proved in 

 Canada to be very barren ; but in the United States the same forma- 

 tion has yielded species belonging to the genera Nautilus, Lituites, 

 Orthoceras, Cyrtoceras, Gomphoceras, Phragmoceras, and Troclioceras. 



Finally, the Guelph Formation of Canada is almost destitute of 

 the remains of Crustaceans. In Wisconsin, on the other hand, 

 Crustaceans are not at all uncommon. Amongst these are such 

 familiar forms as Calymene Blumenbachii, var. Niagarensis ; Illcenus 

 JBarriensis, Murch. ; Geraurus insignis, Beyrich ; and Spharexochus 

 minis, Beyrich. Besides these, there occur new and peculiar forms 

 belonging to the genera Illmnus, Bronteits, Dalmannia, Acidaspis, 

 Leperditia, etc. 



From the above brief review it will be seen that the fauna of the 

 Guelph Formation is to a large extent a peculiar one, many of the 

 known species being restricted to this particular horizon. The most 

 characteristic features in the Guelph Fauna are afforded by the pre- 

 dominance of Trimerellidce and Pentameri amongst the Brachiopoda, 

 the great abundance and variety of the Gasteropoda, and the preva- 

 lence of the remarkable Lamellibranchiate genus Megalomus. These 

 features are so general, that, taken along with the peculiar litho- 

 logical characters of the rock, they justify us in regarding the 

 Guelph dolomites as constituting a distinct series of deposits. At 

 the same time, it is to be recollected that these deposits are clearly 

 only a subordinate stage in the great Niagara Formation, of which 

 they form an integral portion. 



III. — Contributions to the Study of Volcanos. 1 



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



The Great Crater-lakes of Central Italy. 



IN no part of Europe, probably, can we find such striking examples 

 of the effects which may be produced by single paroxysmal out- 

 bursts of volcanic force, as in the band of igneous rocks which stretches 

 through nearly the whole length of the Italian peninsula, on the 

 western side of, and parallel to the chain of the Apennines. Etna 

 and many of the extinct volcanos of this continent constitute, it is 

 true, mountains of vaster bulk than any in the district to which we 

 have referred ; but while the former were evidently built up by the 

 accumulation of the products of igneous forces operating during long 

 periods from the same centres, and with comparatively moderate 

 violence, the enormous craters of the latter bear witness to the occur- 

 rence of single outbursts of these forces of far greater intensity. 

 The materials which have been ejected from the various centres of 

 1 Concluded from page 308. 



