566 ME. 6. W. LAMPLUGH ON THE [Nov. 1 89 5, 



Silurian or older. Their correlation with the Skiddaw Slates of the 

 Lake District seems to rest on a satisfactory basis ; but as the Skid- 

 daw Slates of that region are believed to cover a wide range in time, 1 

 and as our knowledge of their stratigraphy is still very limited, 

 this correlation is of uncertain value. 



Although most observers of the Manx Skiddaw rocks have 

 remarked on the contorted character of the bedding, it is evident 

 that the resultant complexity of the structure has not been realized, 

 and that the strata have been credited with a greater simplicity of 

 arrangement than they possess. Because the beds on the western side 

 of the Island from the coast up to the central hilly axis have usually 

 a northerly or north-westerly dip, while on the eastern side the 

 prevalent dip is to the opposite direction, it has been assumed that 

 the structure is that of a simple anticline. But this interpretation 

 is almost certainly erroneous ; and instead of the rocks of the coast- 

 line having risen, before denudation, as an arch over the central 

 area, it is more probable that the contorted grits and flags so 

 largely developed at the lower levels on both sides of the Island 

 pass, as a highly folded platform, beneath the argillaceous mass out 

 of which most of the central hills are carved. 



Pending the completion of the detailed examination of the whole 

 Island it would be premature to lay too much stress upon this 

 reading of its structure ; but so far as my work has yet gone the 

 supposition agrees best with the observed facts, in spite of some 

 apparent reversals of the general order by which the grits are 

 locally brought uppermost. 



IV. The Distribution of the Crush-Conglomerates. 

 (1) Summary of the Field-evidence. 



For the convenience of the reader who may not require to enter 

 into the local details, I will give a brief summary of the field- 

 evidence before entering into the more circumstantial account of the 

 sections. 



As a result of the intense shearing which the Skiddaw Slates of 

 the Isle of Man have everywhere undergone, actual disruption of the 

 bedding has in certain localities taken place on a very extensive 

 scale. The crush-conglomerate thus formed attains its widest 

 development on the north-western side of the central axis of the 

 Island, north of the valley which cuts the hil] -range between Peel 

 and Douglas, though it is also seen, on a 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 north-north-east for 5 miles, with a probable 

 extension southward for 3 miles farther. It is usually flanked on 

 the one side by gritty flags and on the other by dark clay-slate. 



1 J. E. Marr, Geol. Mag. 1894, p. 122. 



