276 Reports and Proceedings — Geological Society of London. 



(a) The Chalk dominates greatly over the Clay, the latter being 



often merely a local phenomenon. 

 (6) The Chalk is stained brown, and the Clay streaked with chalk 



for a few inches from the junction. 



(c) The Clay is often a mere facing to the Chalk, or occupies 



semi-cylindrical or wedge-shaped cavities, which sometimes 

 seem to terminate above sea-level. 



(d) The Clay seems often associated with superficial ravines, 

 which are probably never much prolonged below the sea- 

 level. The Chalk is strongly folded, but rarely, if ever 

 faulted, and there is no evidence to connect the intercalations 

 of Drift with faults. 



Numerous sections in Eiigen are then described, which (though 

 there are differences in detail) present a general resemblance to 

 those in Moen, and as a rule have no resemblance to those near 

 Cromer. After discussing and rejecting the hypotheses (faulting or 

 folding and the thrust of an ice-sheet) which at present apparently 

 occupy the field, the authors point out that any satisfactory theory 

 must be in accordance with the following facts : — (1) The tripartite 

 and generally orderly arrangement of the Drift (Rugen only) ; 

 (2) the frequent unconformity of the Drift with the Chalk; (3) the 

 occurrence of valleys or clefts in the Chalk ; and (4) the variations 

 in inclination of the Drift-beds, without the loss of their general 

 evenness of bedding. If, at the beginning of the Glacial period, the 

 surfaces of the islands had assumed nearly their present outlines, 

 they may have become permanently covered with snow without the 

 formation of glaciers. Drift might have been deposited on this 

 frozen surface — first clay, next sand, and then another clay. When 

 the climate ameliorated, the more or less frozen Drift would settle 

 down, as the snow underneath it melted, warping and twisting over 

 the crags and projections of the Chalk surface, moulding itself into 

 the depressions, and dropping into the pipe-like hollows, as the snow 

 and ice below gave way. 



The authors abstain from discussing the physical conditions under 

 which the Drifts accumulated. 



2. " A Critical Junction in the County of Tyrone." By Professor 

 Grenville A. J. Cole, F.G.S. 



The investigations of the author have led him to the conclusion 

 that the granite of Eastern Tyrone is identical with that of Slieve 

 Gallion. In the Memoir of the Geological Survey it is shown that 

 the Lower Carboniferous beds near Moneymore are full of fragments 

 of the former granite, while it is considered that the Devonian grits 

 at Aghnacreggan are " vitrified and turned into quartzite " at the 

 junction. The ' quartzite ' appears to be fine-grained yellowish 

 granite, while the Devonian rocks exposed by excavation at the 

 junction are mainly made up of large and small fragments derived 

 from the granite. The granite is therefore of pre-Devonian age, and 

 may be linked with those of Cavan and other parts of Ireland which 

 are connected with the ' Caledonian ' epoch of mountain-building ; 

 but it is possibly even pre-Ordovician. 



