714 DK. HELGI rJETTJESSOX ON [Nov. I906,. 



That there is a great unconformity between the two basalt- 

 formations of Iceland is very well seen on the north side of 

 Snsefellsnes (Western Iceland). Here the Pleistocene basalts, 

 together with sedimentary intercalations in the lofty and precipitous 

 Kirkju Fell, have a thickness of more than 1100 feet. The basal 

 part of the fell is built up of decayed basalts, and cut by thick 

 dykes which terminate against the base of the Pleistocene Series. 

 In Sto% and the headland of Bulandshof Si we also find the basal 

 parts cut by thick basalt-dykes ; while thinner dykes, having another 

 trend, traverse the Pleistocene formation to the top. In the two 

 last-named localities the basal layer of the Pleistocene Series is 

 ibssiliferous, and has, in BulandshoitSi, yielded twenty-two species of 

 mollusca, twenty of which (teste Ad. S. Jensen) represent a highly- 

 Arctic fauna (with Yoldia arctica), such as at the present day is 

 found living along the coasts of Spitsbergen. 



It is a remarkable fact, looking at the very considerable thickness 

 of the Crag of Tjornes, that nowhere else in Iceland has there been 

 found any trace of such Pliocene deposits. And yet the Pliocene 

 sinking of the land can hardly be supposed to have been confined 

 to the comparatively-limited area which is now Tjornes. 



"We shall understand this fact, if we assume that the coast-line of 

 Iceland has receded greatly since Pliocene times — as, indeed, in part 

 can be demonstrated — so that a fringe of Pliocene deposits may have- 

 been abraded everywhere, except in a firth cutting exceptionally 

 deep into the country. 



Pliocene times would seem to have been, in Iceland, a period of — 

 at any rate comparative — quiescence from vulcanicity. Volcanic 

 accumulation was probably succeeded by subsidence, erosion, and 

 sedimentation. Towards the close of the Pliocene, or at the begin- 

 ning of the Pleistocene Period, there followed a revival of volcanic 

 energy, which resulted in the building-up of the Pleistocene basalt- 

 formation — a part of which is the palagonite — or ' tuff- and breccia- 

 formation ' of the older geologists. 



Thus the Pliocene of Tjornes affords most important comple- 

 mentary evidence as to the age of the much-discussed palagonite- 

 formation. But, even from a more general point of view, the 

 richly-fossiliferous Icelandic Crag is, in my opinion, eminently 

 worthy of the attention of geologists. 



I will conclude with the expression of the wish that Science may 

 not have to wait another 20 years for further contributions to the 

 knowledge of the interesting Pliocene fauna of Iceland. 



Discussion. 



The President referred to this remarkable evidence of the con- 

 tinuity of volcanic activity in Iceland throughout a long interval of 

 geological time. The oldest basalts of that island no doubt dated 

 Irom some early Tertiary period like those of our own Western Isles. 

 The Crag-deposits noticed in the present paper, as intercalated 

 among the volcanic sheets, furnished interesting and important 



