474: Mr. Edward Heron-Allen [May 21, 



places several thousands of feet in thickness, across Europe and 

 Xorthern Africa, and through Asia by the Himalayas to China, the 

 matrix, containing the perfect fossils, being a rock formed of their 

 comminuted remains. The deposit is characteristic of the Eocene 

 period ; but the Xnmmulites have now died out, being represented 

 to-day in the tropics l>y a single living species, N. cummingii (SI. 4). 



Coeval with the Nummnlites, and closely approximating to them 

 in importance as world builders, is the genus Alveolina (SI. 5), 

 which is found in the same beds either gradually replacing them, or 

 sometimes taking their place with startling suddenness in the strata. 

 Off the extreme point of Selsey Bill, in Sussex, the locally named 

 "Mixon reef" rises at the summit of the Eocene deposits, composed 

 almost entirely of fossil shells of A. hoscH (SI. 6), indistinguishable 

 from the living shells of the species which abound to-day in the 

 shallow water and littoral sands of Australian and other tropical 

 shores.^ 



With all respect, however, to the recent utterances of its most 

 noteworthy protagonist,- the Nummulite is a mere parvenu com- 

 pared with the species SpiriUina groomii (SI. 7), discovered in the 

 Cambrian rocks of Malvern by Chapman,^ and rediscovered by 

 Arthur Earland and myself alive in the shallow waters of the We-t 

 of Ireland,"^ which probably represents the earliest specific form of 

 life to be found living at the present day. Even the conservative 

 little Lingula shell has become slightly modified since its earliest 

 ancestors wallowed in Cambrian mud a hundred million years ago.-^ 



I have alluded to the Globigerinae (SI. 8), which are to-day 

 forming a geological deposit of unknown thickness over 48 millions 

 of square miles in the modern oceans.'' Agassiz has observed (SI. 9) 

 that " no lithological distinction of any value has been established 

 between the chalk proper and the calcareous mud of the Atlantic," " 

 and it has been estimated that the time occupied by the deposit of 

 the English chalk, arguing by the rate at which the Atlantic ooze 

 is formed (which is about one foot in a century), must have beeai 

 150,000 vears.s 



^ E. Heron-Allen and A. Earland, The Foraminifera in their role as World- 

 Builders. Journ. Quekett Micr. Club, ser. 2, vol. xi. pp. 9-11. 1913. 



- R. Kirkpatriek, The Nummulosphere. London, 1913, etc. 



^ F. Chapman, I'oraminifera from an Upper Cambrian Horizon of the 

 Malverns. Q. Journ. Geol. Soc, p. 257. 1900. 



•• E. Heron-Allen and A. Earland, The Foraminifera of the Clare Island 

 District. Proc. R. Irish Acad., vol. xxxi, (Clare Island Survey, pt. 64), p. 107, 

 pi. ix. figs. 2, 8. 1913. 



^ Cf. E. Heron-Allen, Selsev Bill. London, 1911, p. 24. 

 Sir. J. Murray, The Ocean, p. 207. London, 1913. 



" A. Agassiz, Three Cruises of the Blake, vol. i. p. 150. London, 1888. 



^ A. J. Jukes-Brown, Handbook of Physical Geology, p. 130. London, 1884. 

 The rate of deposition varies slightly according to deptli. See Murrav, op. cit. 

 p. 224, 



