334 Reports and Proceedings — Geological Society of London. 



fragments of limestone, and the various mineral aggregates derived 

 by metamorphism from it, are met with, but they are chiefly re- 

 €ijected old ejected blocks. A light-green spongy tachylite is also 

 frequent. 



The ' essential ejecta,' either as scoria or lava, do not show any 

 marked difference from the usual products of Vesuvius in such 

 eruptions during the last three centuries. 



Although much damage has been done, great areas of rugged lava 

 surfaces that would have required centuries to render cultivable, are 

 now available for the growth of woods, viues, and herbaceous plants. 



III. — June 13th, 1906. — Sir Archibald Geikie, D.C.L., Sc.D., 

 Sec. E.S., President, in the Chair. The following communi- 

 cations were read : — 



1. " Recumbent Folds produced as a Result of Flow." By 

 Professor William Johnson Sollas, Sc.D., LL.D., F.R.S., F.G.S. 



Professor Lugeon, in his treatise on the pi'e-Alps of Chablais, has 

 described a series of recumbent folds so greatly exceeding in 

 horizontal extension their vertical thickness, that they are commonly 

 spoken of as sheets rather than folds ; they lie with remarkable 

 flatness one on the other, and, as a rule, those higher in the series 

 extend farther to the front than those below, a feature referred to as 

 'deferlement.' The roots of several of the lower of these folds are 

 visible in the high Alps adjacent, but the roots of the higher folds, 

 which form the pre-Alps, must be sought in the zone of Mont 

 Blanc and the Bx-ian^ontiais. Thus some of the uppermost folds 

 may have surmounted the obstacle presented by Mont Blanc, on 

 their way to the front in the pre-Alps. Many of the features 

 presented by recumbent folds are more suggestive of flowing than 

 bending. Experiments have been made with pitch-glaciers (poissiers) 

 in which an obstruction had been placed. In this way folds were 

 produced, one of which was not unlike the Morcles fold behind the 

 Diablerets, another was like the Pilatus, and yet another like the 

 Sentis, and the fourth compared with the overslide of the Bavarian 

 front ; all four exhibit deferlement. In this experiment the lower 

 limb of each fold is adjacent to the similar limb of its neighbours ; 

 but in another experiment, in which two obstacles were used, the 

 results were nearer to those seen in the mountains where the lower 

 limb of a superior fold reposes on the upper limb of the fold 

 immediately beneath it. Movement of this character may possibly 

 explain the want of continuity of certain beds at the conclusion of 

 the movement. 



2. " The Crag of Iceland — an Intercalation in the Basalt 

 Formation." By Dr. Helgi Pjetursson. (Communicated by 

 Professor W. W. Watts, M.A., M.Sc., F.R.S., Sec. G.S.) 



The existence of fossiliferous deposits on the west coast of Tjornes, 

 Northern Iceland, has been known for nearly 160 years. Morch 

 enumerates 61 species of moUusca, and concludes that the temperature 



