O'Heilly — De UosHi'a Sdnmical and Eiidodijnamkal Map. 461 



He considers (p. 9) that the seismieal map is not sufficient for 

 the objects of his studies, which must be extended to all the phe- 

 nomena having an origin internal to the surface of the earth, in 

 order " to prepare from them a synthesis which will reveal the 

 secrets of telluric dynamics — of that telluric dynamics up to the 

 present so very little studied and not at all known, although it 

 covers so many menaces for our very existence as well as innume- 

 rable aids to our prosperity." 



Speaking of Pella's definition of an earthquake as an attempt, 

 or unsuccessful effort of eruption from the interior of the earth, 

 he says : "As a matter of fact, there never is a volcanic eruption 

 without earthquakes, nor is there an earthquake, even in non- 

 volcanic regions, without eruption or at least emission of gases and 

 vapours." 



Having alluded to microseismical movements and their micro- 

 eruptions, he says : " In one word, the subterranean circulation of 

 water is to be considered as a factor of the first importance in the 

 incessant labour of the internal agents of the globe." 



Speaking (p. 12) of the method which he proposes to employ 

 for the co-ordination of his work : — " The system of division, the 

 best appropriated to the scope of my undertaking, is that of con- 

 sidering separately the hydrographic basins of Italy. This divi- 

 sion, from what has been already explained, leads mechanically, 

 so to speak, to tracing out the network of the fissures and of the 

 seismic radiants, and to defining the axes of the valleys, along 

 which will be found the secondary manifestations of activity, the 

 thermal springs of the present, and the geological traces of a telluric 

 action which has ceased to show itself." 



He shows (p. 13) that the surface hydrography of the country 

 is intimately connected with internal telluric action, and adds : "If 

 the valleys are in the most cases fissures of the earth's crust [molo] 

 they must, consequently, be the passages by which absorption of 

 the surface waters takes place, so as to reach directly the internal 

 laboratories and join the subterranean system of circulation." 



Alluding (p. 14) to the frequency of earthquakes in and about 

 the Lago di Grarda, he states : " The most recent geological re- 

 searches have demonstrated that the lake is an immense geological 

 fissure. . The courses of the great rivers are very frequently the 

 axes of earthquake shocks. Whence," he says, " the study of the 



SUIEN. I'iCOC. K.D.S. — VOL. iV. VT. VUI. 2 li 



