24 PEOCBEDTITGS OF THE GEOLOGICAL SOCIETY. [NoV. 20, 



volcanic scorioc near the Cliksa Madre and the iN'orman Tower, which 

 are close to the source of the lava- stream, are further proofs to en- 

 able us to fix accurately the site of the crater, Avhile the moveable 

 materials which form its outer sides have been carried away by the 

 action of waters. 



There can be no doubt that this doleritic rock oiFers a smaller 

 number of phenomena than that of Paterno, in consequence of its 

 smaller diameter and the ground being more changed ; but it is more 

 interesting on account of the clear connection which the volcanic 

 products show with the pre-existing sedimentary formation which 

 has not been invaded by lavas from Etna. The pleistocene clay and 

 the post-pliocene conglomerate are closely connected together on the 

 west and north-west sides, where no kind of alternation can be seen 

 between these two rocks — either the volcanic or the sedimentary — as 

 occurs in many other cases of extinct volcanos in the Yal di Note 

 and in the Yallone della Pulicera, in which the stratification of the 

 sedimentary deposit can be distinctly seen for a great distance ; the 

 clay and the conglomerate are perfectly horizontal. 



Conclusion. — From these observations we may conclude, — 1st. 

 That at Paterno and Motta (Sta. Anastasia) are the remains of two 

 doleritic volcanic cones, because we there find the essential elements 

 of volcanos, viz., a central nucleus, lava, and fragmentary materials. 

 2nd. That these volcanic i^henomena were contemporaneous, and oc- 

 curred during the post-pliocene period, previous to the deposit of the 

 freshwater calcareous tuff of the neighbourhood of Paterno, because 

 in the fragmentary materials of the two cones we find clay and 

 pebbles of sandstone (gres) — pre-existing rocks, and no calcareous 

 tufi*. 3rd. These are cones of eruption and not of elevation, as some 

 persons have lately endeavoured to prove, because the pre-existing 

 sedimentary deposits of the neighbourhood do not show any modifi- 

 cation in the direction of their strata. 4th. These eruptive cones are 

 independent of Etna, because the doleritic nuclei have been brought 

 up at once from below, and the lavas have issued from their terminal 

 portions ; whereas in all the parasitical cones of Etna the streams 

 follow the direction of the longitudinal fractures, which extend from 

 the volcanic axis to the periphery ; and the lavas do not issue from 

 the upper portion of the parasitical cones, but from their bases, or at 

 some greater distance. The bursting forth of lava from the throat 

 or crater is a peculiarity of central eruptions, but not of those which 

 are lateral or parasitic. 



