80 Notices oj Memoirs — The St. Gofhard Tunnel. 



tlie pebbles, but also in otliers, leading to movements along lines of 

 least resistance, bj' wliicli the pebbles would become j)acked as closely 

 as possible together. The quartz grains lying between the pebbles 

 would then not only be pressed against, but also dragged over them. 

 As they began to more, they would produce a delicate almost imper- 

 ceptible striation, but with continued progress this would deepen, the 

 grit would " bite " more deeply into the stone, and would at 

 length become too far imbedded to overcome the resistance in front ; 

 then it would be brought to a sudden standstill, and remain as we now 

 find it implanted at the end of the trough which it has excavated. 



The history of the pebbles is then as follows : the Carboniferous 

 Limestone, which crops up close to Portskewet around Chepstow, 

 was denuded in Triassic times, and furnished material for a beach of 

 rounded and polished pebbles on the shores of the Triassic sea ; 

 subsequent deposits, probably including Jurassic and Cretaceous 

 sediments, were superimposed upon this beach, and under the con- 

 siderable pressu7-e which resulted the pebbles were packed closely 

 together, forced one into the other, and pitted all over with imbedded 

 sand grains ; lateral movements dragged along the sand grains over 

 the surfaces of the pebbles, scoring them with delicate furrows and 

 sti'iee. Subsequently the dolomitic jDaste between the pebbles 

 cemented into a hard matrix, and bound the whole together into a 

 conglomerate. 



In a note read before the British Association last August, I showed 

 that certain fragments of limestone in a Triassic breccia retained the 

 striation (slickenside) that had been impressed upon them before 

 they were detached from the parent rock and deposited in their 

 present place. We now find an instance of a contrary kind, in 

 which the strige on imbedded pebbles have been produced subsequent 

 to deposition ; but in neither case could an experienced observer be 

 deceived for a moment as to the real nature of the striation ; glacial 

 action is here indeed altogether out of the question. It might be 

 thought that the glacial origin assigned to the striations on certain 

 fragments of stone from the Old Eed Sandstone and Permian 

 deposits, is called in question by these observations ; the exact con- 

 trary is, however, the case ; since while we have shown that striation 

 may be produced on included fragments in other ways than by the 

 action of ice, we have at the same time shown that no difficulty need 

 be felt in distinguishing such striation when it occurs. 



nsroTioiES o:p n\d::Ei]yi:onas. 



The Mont St. Gothaud Tunnel. 

 Sulle condizione geologiche e termiche della grande galleria del 

 S. Gottardo. Nota dell' inq, F. Giordano, Boll, del R. Comit. 

 Geol. d'ltalia. Sept. and Oct. 1880, Vol. XL 



IN the last Bolletino Inspector F. Giordano gives alengthy report 

 on the geological conditions of the St. Gothard tunnel, and many 

 of the facts and particulars he tells us are drawn from the various 

 published papers of the late chief engineer Stapff. Particulars are 



