62 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



forming the foundation of the island is very difficult to 

 determine owing to the absence of undoubted fossil 

 remains and the alterations due to heat, pressure and earth 

 movements. The " Manx slates "which build up its back- 

 bone from Bradda Head to North Barrule (fig. 1, Map) are 

 however certainly not later than Lower Silurian, and are 

 placed by Mr. Lamplugh in his recent Memoir* as Upper 

 Cambrian, with a query ; and this central ridge which 

 constitutes the mountain ranges seems to have been an 

 insulated mass even as early as 'the beginning of the 

 Carboniferous period. " This prototype of the present 

 island appears afterwards to have been enfolded and 

 obliterated by the sediments of later times ; but with the 

 process of denudation the old ridge has once more emerged 

 from beneath this mantle." The physical features of the 

 district, such as are necessary for an understanding of the 

 past history, can best be given by quoting a few para- 

 graphs from Chapter I. of Mr. Lamplugh's authoritative 

 Memoir, as follows: — 



" Its insular character is as well maintained in its 

 physical as in its geological features. The erosive agency 

 of the simple drainage system descending radially to the 

 sea from the central hill-range, together with that of the 

 waves which surround it, is adequate to explain all the 

 contours of its present surface. It must indeed fre- 

 quently during its history have been re-united to the 

 mainland by a continuous land surface ; but at such times 

 it probably still retained in some degree its characteristic 

 individuality, and arose above the surrounding plain as a 

 hilly tract with a self-contained drainage, although its 

 streams may then have been tributary to a larger river- 

 system lying beyond its limits." 



* The Geology of the Isle of Man, by G. W. Lamplugh : Memoirs 

 of the Geological Survey, 1903. 



