98 Transactions. 



This comparatively wide area must Lave liad, at some remote period, 

 a steppe or semi-desert climate, under whose influences a xerophytic and 

 partly calciphile flora developed and flourished, and it is likely that what 

 we now have represents only a portion of this flora, many species having 

 probably died out altogether. 



This area must have been partly a peneplain (upon which alone 

 R. paucifolius, it would seem, could " originate " and flourish), and would 

 probably be conterminous with a range or ranges of hills with limestone 

 rocks exposed and weathering into dust exactly as they now do on the 

 small area here under observation. But such peneplain need not have 

 consisted entirely of Tertiary limestone beds. 



The area would be in the nature of a strip or belt, -of no very great 

 width and probably much interrupted, corresponding roughly to the shore- 

 line or lines of the hypothetic Tertiary sea or seas. It would be con- 

 terminous with and more or less alternated with an area or areas of 

 pre-Tertiary formation, probably lying to the -north and east, as posited, 

 e.g., by Cockayne (1911, pp. 343-44), by way of which probably the 

 mesophytic flora would return when a more humid climate should prevail 

 in this area. Upon this pre-Tertiary area the related species, R. chordo- 

 rhizos, &c., would have originated and flourished, or that single species or 

 form from which they and R. pancifoliics trace their common descent. 



The greater part of these limestone beds" was destroyed by erosion of 

 various kinds in subsequent ages, leaving only the present small isolated 

 remnants, of which the Trelissick Basin is one of the largest. 



It is impossible that by the elevation of the land 3,000 ft. or 4,000 ft. 

 (Haast, Hutton, Park), and the consequent refrigeration and glaciation, 

 the whole flora of the district (as has been thought) was driven to another 

 tract, now non-existent, and returned with the subsidence of the land and 

 consequent change of climate. " Return " of a calciphile flora over areas 

 upon which the Tertiary beds had been destroyed would be impossible, 

 especially since, as we have seen, this flora as a unit is not a "traveller"; 

 and we cannot escape the conclusion that this plant community has been 

 represented within the area of the small basin, since it first established 

 itself or " originated " in that neighbourhood. 



Glaciation bears upon the question in two ways : — 



(1.) Hutton (1900, p. 176), followed by Cockayne, correlated the sup- 

 posed drought epoch, of which our flora shows signs, with the glacial epoch, 

 which he placed in the older Pliocene period. This view was adopted by 

 Cocka}Tie (1901, pp. 280 et seq.) ; but that authority believed that at the 

 height of the glaciation the eastern mountains (within which this area is 

 included) might still support a xerophyte flora like that of the shingle-slips 

 of the present day (Cockayne, 1911, pp. 348 et seq.). 



The view of Speight (1911) and others is that- the last glacial epoch is 

 much more recent, that the drought period was correlated with it (Cockayne, 

 1911, p. 344), that the Tertiary deposits were continuous over a much 

 larger area than is the case now (Speight, 1915, p. 354), that the Castle HiU 

 area probably escaped glaciation altogether (Speight, 1917, pp. 323 et seq.), 

 and that the Trelissick Basin at the height of glaciation was " probably 

 a snowfield " (Speight, 1917, p. 323). 



It would seem certain that a steppe climate or period of drought must 

 have obtained here over a large area at least once (probably more than once) 

 since Tertiary times, but to the present writer it seems quite uncertain 

 whether this was coeval with and resultant from the glacial epoch or not 



