30 TYPE AMMONITES—IV Feb. 



half, which ^delded. the giants, are nearly worked out, there is little chance 

 of obtaining further specimens. 



The giants, sadly weatherworn, standing outside the office, seemed 

 from casual examination to represent the genera Titanites, Briareiies, 

 Gigantites, Trophonites and some forms not yet known in Buckingham- 

 shire. Other forms, among them presumably Galbanites, were noted 

 outside houses ; but no specimens comparable with the species obtained 

 in Buckinghamshire from the Upper Witchett and the Old Osses Ed 

 came under my observation. This suggests that in the Midlands there 

 are preserved Portlandian (Gigantitan) strata of later date than those 

 of Portland. 



The strata known as Kimmeridge Clay, or Kimmeridgian, with 

 their contemporaneous deposits in other countries — White Jura and 

 Tithonian, partly — present the puzzle in another form. The English 

 Kimmeridgian Beds, excepting the subordinate series at the top — the 

 Hartwell Clay, which " is some 30 feet thick at Bieiton, near Aylesbury, 

 but has not yet been bottomed " (workman), appear to give, in spite 

 of considerable local differences of thickness, a fairly uniform faunal 

 sequence. More detailed analysis may cause this idea to be modified ; 

 but at present the impression given is that such earth-movements as 

 troubled the Kimmeridge Beds belonged to a series of wide-arched 

 waves, each one raising or depressing England as a whole, but that 

 such movements as disturbed the later beds, say, from Hartwell Clay 

 onwards, took the form of narrow waves of local intensity, raising or 

 depressing small areas of England. 



The puzzle in the case of the Kimmeridge Beds, therefore, is not, 

 as in the case of the Portland Beds, the difficulty of correlating the 

 strata of one parish with another ; it is concerned with a still harder 

 task — the comparison of English strata with those of distant localities —  

 mainly, for instance, with Wurtemberg. Only occasionally do the 

 Ammonite faunas of England and Wurtemberg correspond — generally 

 there is a most marked difference between them. Two theories may be 

 held, (i) in Kimmeridgian times England and \\'urtcmberg belonged 

 to distinct zoological provinces, (2) that they belonged to the same 

 province, but the faunal differences are the product of penecontempo- 

 raneous erosions, affecting first the one area and then the other, more 

 or less alternately. 



Against the first theory may be set the following argument : — 

 The similarity in numbers of Ammonite species and specimens in England 

 and Wurtemberg during most of the Ammonitoidic Period involves the 

 conclusion that the two areas formed part of one province during such 

 times. Erom the Caloceratan to early Zigzagiceratan and from Macro- 

 cephalitan to early Cardioceratan the Ammonite features are similar. 

 Erom Zigzagiceratan to Macrocephalitan they are different — there is 

 poverty in the English area, due, possibly, to insufficient salinity of the 

 sea rather than to any definite barrier. Erom Cardioceratan onwards 

 each area is about equally rich in Ammonites ; but there is a marked 

 difference in the species. At first sight, division into two provinces 

 seems to be the explanation ; but sudden divorce, in the Cardioceratan 

 Age, of such a long-standing partnership should not produce such 

 differences : they are too great. The Ammonites left each side of the 

 barrier parting the provinces should continue their respective develop- 

 ments in the two areas, producing not forms which were identical, 

 because the conditions would not be identical, but forms which were 



