584 MR. G. W. LAMPLTTGH ON THE [Nov. l8o,5 r 



grit-bands, by thermal metamorpbism, although not visible in con- 

 tact with any igneous mass (see Mr. Watts's Appendix, p. 590) ; but 

 within the strike of this zone the chief granitic outbursts of tbe 

 Island occur ; and I am hoping that it may hereafter be found 

 possible to bring into intimate connexion the whole of these 

 phenomena. 



In my attempts to make out the direction of the fluxion-move- 

 ments during the formation of the crush-conglomerates I have not 

 been very successful. The later shearing which the rock has 

 undergone and the contortions into which it seems to have , been 

 thrown during and after the brecciation, render the results un- 

 certain. Tbere is a very general elongation of the inclusions in the 

 direction of strike, but I am not sure Whether this took place during 

 the earlier or the later movements. The force which caused this 

 elongation seems usually to have acted from the N.E. to the S."W. 

 points. In a few instances I have thought that there were vague- 

 indications of a primary S. or S.E. to N". or N.W. movement of the 

 larger inclusions, but these are quite insufficient to give a basis 

 for generalized statement. The solution of this point also will 

 probably be found in the study of the Skiddaw rocks of the Island 

 as a whole. 



(2) The Age and Duration of the Crushing. 



Within the limits of the Isle of Man there is scanty evidence 

 whereby to fix the age of the formation of the crush-conglomerates. 

 Since the earth-movements affected the slate-rocks as a whole, the 

 period must have been of later date than the deposition of the 

 uppermost beds of the Skiddaw series ; but in the present state of 

 our knowledge this does not enable us to go further than to state 

 that the crushing must be of later date than Cambrian times, or 

 perhaps than Lower Silurian. The only available upward limit is 

 that to be found in the relation of the slate-rocks to the Basement 

 Conglomerate of the Carboniferous strata on Langness, where the 

 character of the unconformability is such as to show clearly that 

 the Skiddaw Slates had assumed their present structure and aspect 

 before Carboniferous times. 



Within these wide limits the Island supplies no closer data ; but 

 in the not far distant and structurally connected regions of the 

 Lake District, the east coast of Ireland, and the Southern Uplands 

 of Scotland we know that very extensive earth-movements, affecting 

 rocks of similar age and characterized by similar intensity of 

 plication, took place at the close of the Lower Silurian epoch, and 

 were renewed after the deposition of the Upper Silurian strata. 



With regard to the duration of the pressures, I think there 

 is abundant evidence in tbe crush-conglomerates themselves that 

 the brecciation was not produced suddenly, but by a force acting 

 slowly, and probably intermittently, during a considerable period. 

 The beds seem first to have been thrown throughout into acute 

 plications, during the formation of which there was time for an 



