TRANSACTIONS OF THE SECTIONS. 95 



On Spheroidal Structure in Silurian Rocks. By the Eev. J. D. La Totjche. 



Spheroidal masses of various sizes are frequently met with in the Siliman and 

 seme other rocks. In the Wenlock shale smaller nodules, an-anged in lines with 

 the regularity of bricks in a wall, as well as huge masses of rich limestone, called 

 ball_ stones, may be observed. These latter concretions give plain evidence of 

 ha-i-ing been formed subsequently to the deposition of the whole stratum, inas- 

 much as they have disturbed the lines of stratification both above and below. A 

 discoloration, owing to the inhltration of moisture, is often found to accompany 

 nodular sh-ucture. The section of an oblong piece of Caradoc sandstone has been 

 found to exhibit three bands alternately of yellow and blue stone, the former appa- 

 rently more sandy than the latter. Here not only the coloming, but the physical 

 character of the stone seemed to have undergone a change from the effects of wea- 

 thering. A railway- cutting at the southern extremity of the Longmynd presents 

 an instructive example of the same kind. The cubical masses of rock almost 

 invariably weather into spheroids, the form of which is indicated by fine lines on 

 the faces of the stone, long before the edges fall oft" and reveal their perfect shape. 



Another veiy beautifid instance may be seen in the Whitclifle, near Ludlow, 

 where three large spheroids, of several feet in diameter, appear enclosed in concen- 

 tric layers of Upper Ludlow rock, which suiToimd them like the coats of an onion 

 the stratification of the general stratum, however, passing through them. 



Has this peciUiar structure been the result of an original deposition of nodules 

 or calcareous matter at certain spots,- or is it owing to more recent causes ? 



The fact that the shape of nodides fi-equently depends on the shape of the masses 

 in which they are contained, and that their position is determined by joints in the 

 rock, also that weathering produces a certain physical change in rocks, rearran- 

 ging to some extent their materials, would lead to the latter conclusion. It would 

 appear that if a quantity of soluble or crystallizable matter is equally distributed 

 through a large mass, and that some external agent, such as moisture, is brought 

 to bear on it, it may drive inwards the more soluble constituents, produce those 

 concentric layers above alluded to, and in many cases be the cause of a central 

 nodule. 



If this be so, we have here further evidence of an incessant change and motion 

 among the particles of the apparently motionless rocks, suggesting that some 

 important results are taking place in them, slowly, in immense periods of time. 



Notice of remarl-ahle Glacial Strice latehj exposed at Portmadoc. 

 By Jonjf Edward Lee, F.S.A., F.G.S. 



The object of this notice was to bring before the Section the fact, that probably 

 one of the best specimens of glacial action had lately been exposed in the small 

 town of Portmadoc, and will very shortly be destroyed, the locality being wanted 

 for building-sites. The part now exposed is about 100 feet wide by 50 feet long • 

 many of the strife can be traced the whole length. It is nearly a plane, with the 

 exception of a furrow about 13 inches deep in the middle. Most of the strife run 

 from S.E. to N.W., but a few run from S.S.E. to N.N.W. (magnetic). The ano-le 

 of inclination varies from 14J to 16°. ° 



As the plane slopes to the N.W., and the hill behind is comparatively low, 

 while the highest gi-ound in the neighbourhood is almost immediately in front 

 though on the other side of the vaUey, it would appear that if the glacier which 

 caused these strife originated in the highest gi-ound, it must have taken a sudden 

 turn when nearing the shore. If this is not thought probable, there must have 

 been two sets of glaciers meeting in the valley. 



Denudation of Western Brittany. By G. A. Lebotjr, F.R.G.S. 

 The conclusions brought forward in this paper are as follows : — 

 1. That, with the exception of a central range of hills of elevation, Western Brit- 

 tany consists of two great plains of viarine denudation. 



