I 



Intelligence and Miscellaneous Articles. 395 



mcnt on the north side of the central valley, though it is noted on 

 a more limited scale in a few localities farther south. It is well 

 exposed in the cliffs 3 miles north of Peel, but the finest sections 

 are in the interior in Sulby Glen, where the structure has a 

 thickness of some hundreds of feet, and runs continuously about 

 north-north-east for 5 miles, with a probable extension southward 

 for 3 miles farther, and also eastward for other 4 miles. It is 

 usually flanked by gritty flags on one side, and by dark clay-slates 

 on the other. It is affected by a strain-slip cleavage later than the 

 brecciation, and several igneous dykes which intersect it are affected 

 by the same cleavage, though not by the brecciation-movement. 



East of Sulby Glen the structure extends towards Ramsey, at 

 first in a horizontal spread over a mile in width, and afterwards in 

 a series of comparatively narrow subparallel bands, and it is sug- 

 gested that we are dealing here with the emergence of a deformed 

 plane. The structure is continued eastward into the hill overlooking 

 Ramsey, beyond which it is cut off by the sea. In this locality, as 

 elsewhere, the sections show the gradual smashing into fragments 

 of highly contorted strata until every trace of the original bedding 

 is lost, and a ' crush-conglomerate ' with lenticular and partly 

 rounded inclusions is formed. 



The rocks described in Mr. Watts's Appendix are grouped in four 

 classes. Firstly, the grits and slates which have been crushed 

 but have not been cou verted into crush-conglomerates ; secondly, 

 the crush-conglomerates themselves, and the fragments which they 

 contain ; thirdly, the dykes of decomposed dolerite (greenstone) 

 and fresh later dolerite which penetrate the conglomerate ; fourthly, 

 a portion of the crush-conglomerate metamorphosed by these in- 

 trusions. 



The chief point of interest is brought out by the examination of 

 the fragments in the conglomerate. All stages of crushing may be 

 traced, until the grit-fragments have a structure which is a mere 

 miniature of the crush-conglomerate itself; that is to say, if the 

 crush -conglomerate be regarded as made of 'fragments' of hard 

 rocks enclosed in crushed ' matrix ' of soft rocks, a host of inter- 

 mediate varieties with varying resistances will occur. Whether 

 any particular one of these varieties shall pass into ' fragments ' or 

 'matrix' under the crushing will depend upon the amount of the 

 crushing force and upon the association (paragenesis) of the material 

 brought together to be crushed. 



XXXIY. Intelligence and Miscellaneous Articles. 



A SIMPLE METHOD OF DETERMINING THE DURATION OF 

 TORSIONAL OSCILLATIONS. BY R. W. "WOOD. 

 TN what follows I wish to describe a method by which the time of 

 -*- torsional oscillations may be conveniently observed, for instance 

 that of a magnet in determining the horizontal intensity of terres- 

 trial magnetism. The usual methods labour under the drawback 

 that the watch and the oscillating body cannot be simultaneously 

 observed. In the present method the watch is brought into the 

 field of view of the telescope with which the vibrations are observed. 



