﻿176 Geological Society. 



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 Brianconnais. 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 con- 

 clusion of the movement. 



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

 Formation.' By Dr. Helgi Pjetursson. 



The existence of fossiliferous deposits on the west coast of 

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

 Morch enumerates 61 species of mollusca, and concludes that the 

 temperature must at that period have been much milder than at 

 present. Gwyn Jeffreys and Searles Wood, from the shells, con- 

 sidered that the deposit could not be younger than Middle Bed Crag, 

 but Mr. Starkie Gardner was inclined to assign a greater age to it. 

 Dr. Thoroddsen thinks that these Crags are younger than the ' Old 

 Basalts ' of Tiornes. The author finds, however, that, at a height 

 of about 500 feet above the sea, they are overlain by the ' Eastern 

 Basalts,' and are indurated and altered by them. Thus there is a 

 fossiliferous intercalation, over 500 feet thick, occupying part of the 

 great gap between the Tertiary and the Pleistocene rocks, the latter 

 containing indurated ground-moraines. The basal layer of the 

 Pleistocene Series is fossiliferous, and has yielded 22 species of 

 mollusca, 20 of which represent a highly-arctic fauna (with Yoldia 

 arctica), such as is, at the present day, found living along the 

 coasts of Spitsbergen. Certain of the larger basalt-dykes are cut 

 off at the base of the Crag. The absence of the Crag-deposits from 

 other localities is explained by the erosion of the coast-line. 



