Vol. 51.] CRUSH-CONGLOMERATES OF THE ISLE OF MAN. 587 



extent, cleaved so as to crumple the hard beds and thrust the 

 cleaved slates into the folds.' 



Two years later Prof. Hughes again mentions the subject in a 

 paper ' On the Altered Rocks of Anglesey,' 1 in which are the fol- 

 lowing suggestive passages (pp. 341 and 342) : — ' When we have 



subordinate hard unyielding beds which are incapable of 



extension, they are broken up and discontinuous ' ; and again (on 

 p. 344) : — ' When on a small scale nodules, or on a large scale 

 masses, of bard rock lying in compressible shale are subjected to 

 contortion, the shale is squeezed out over the harder masses, pro- 

 ducing a kind of fault all round between the harder and softer rock, 

 and giviug rise to slickensides and similar phenomena,' etc. 



In 1883 Prof. T. Bonney, in a paper in this Journal, 2 described 

 and figured the first stages of the breaking up of grit-bands inter- 

 bedded with slate, the phenomena resembling those dealt with in 

 the Appendix to the present paper. 



In America Mr. C. R. Van Hise has described 3 a 'friction- 

 conglomerate ' 10 feet wide, in the Baraboo Quartzite of Central 

 Wisconsin, ' the fragments having been ground against one another 

 until they have become well rounded ' ; and furthermore, we read 

 that ' the rock has been affected by at least two dynamic move- 

 ments, separated by a considerable interval of time.' 



It is probable that there are records of other instances abroad 

 which have not come under my notice. 



Attention may also be called to a short description of similar 

 structures in the recently-issued ' Petrology for Students ' 4 by 

 Mr. Alfred Harker.— July 18th, 1895.] 



VII. Concluding Summary. 



The chief points brought forward in this paper may be epitom- 

 ized as follows : — 



(i) In the Skiddaw Slates of the Isle of Man strata of con- 

 siderable thickness have been locally broken up under 

 shear-pressure, and re-arranged in the form of a crush- 

 conglomerate or friction-breccia. 



(ii) This crush-conglomerate occurs in definite bands striking 

 with the surrounding rocks, sometimes continuous for 

 many miles. 



(iii) The brecciation has usually taken place along the junction 

 of arenaceous with argillaceous strata, and has chiefly 

 affected the passage-beds between such rocks. 



1 Proc. Cambridge Phil. Soc. vol. iii. pt. viii. (1880) p. 341. 



2 Quart. Journ. Geol. Soc. vol. xl. (1884) pp. 19, 20, and fig. 9 with pi. i. 



3 ' Some Dynamic Phenomena shown by the Baraboo Quartzite Eanges of 

 Central Wisconsin,' Journal of Geology, Chicago, vol. i. (1893) pp. 351-52. 



4 8vo. Cambridge, 1895, p. 281. 



