70 Dr. F. H. Hatch—Soda-Felsites in Wicklow. 
phenomenon must be referred to some peculiarity in the disturbances 
to which the rocks have been subjected. 
To explain it, we must go to North Devon, a district, like North 
Wales and the Ardenne, deeply affected by great lateral pressures 
operating on the solid rocks. At various points of the coast east of 
Ilfracombe we find among the slates beds of limestone exhibiting a 
succession of swellings and constrictions analogous to those already 
described ; and we see that this disposition is due to the welding 
together of the adjacent limbs of sigmoid folds under a powerful 
thrust. The stages of the process are clearly exhibited. After the 
formation of a series of S-shaped flexures in the ordinary manner 
(Fig. 1), the direction of the pressure relatively to the bed has 
4 ‘ 3 4 
changed, and the folds have been pressed upon themselves in the 
fashion indicated in Figs. 2 and 3. A node corresponds to the 
attenuated middle limb of a fold, while a ventral segment represents 
the union of the complementary parts of two adjacent folds. 
It appears probable that the process indicated is also that by 
which the varying thickness of the greenstone dykes and the 
quartzite beds has been brought about. It is also seen in various 
stages in thin bands of grit in the Ilfracombe district. It is not 
necessary, however, to suppose that the sharp sigmoid folds must be 
actually formed as a preliminary stage. A series of slight undula- 
tions, as in Fig. 4, affected by a shearing motion in the direction 
shown by the arrows, might equally give rise to the alternate nodes 
and swellings of Fig. 3. 
V.—On tHE Occurrence or Sopa-Frensires (KERATOPHYRES) IN 
Co. Wicktow, IRELAND. 
By Freperick H. Harcu, Pu.D., F.G.S. 
(Communicated by permission of the Director-General of the Geological Survey.) 
N an Appendix to the Explanatory Memoir on Sheets 138 and 
139 of the Map of the Geological Survey of Ireland (Dublin, 
1888), I have given some notes on the petrographical characters of 
the igneous rocks of Co. Wicklow. One or two of the facts elicited 
by an examination of these rocks are sufficiently interesting to 
deserve a wider circulation. 
Associated with various types of greenstone, which will form the 
subject of another communication, there occur in the Lower Paleozoic 
strata of this district (Bala) numerous beds of felsite. These are 
