25 
deposits containing Macrocephalitids ( Macrocephalites ) though they have 
world-wide distribution are not truly synchronous and cannot be cited as 
evidence for wide dispersal of a particular fauna at a given date. How 
many hemerse may be represented by all the deposits preserved at certain 
places, how wide was the distribution of any one constituent of Maero- 
cephalitidae, are all subjects for future investigation when the members 
of the family and their deposits have been properly analysed. 
But though the idea that the deposits found in nearly all parts of the 
globe containing Callovian “ Macrocephalites ” are strictly synchronous 
must be abandoned, so far as the synchronization is concerned, yet it 
remains true in regard to the wide geographical occurrence — only this 
wide occurrence is due not to a great synchronous submergence but to the 
fact that “ Macrocephalites” lived during a time of far greater extent than 
had been allowed for. During such time many physical changes could 
occur, new areas could be opened up, while partial or complete destruction 
of Macrocephalites deposits could take place in other areas. The longer 
the time for making the record, the greater the possibility that it is frag- 
mentary — it would have greater chance to suffer from penecontemporan- 
eous erosions. 
That the idea of synchronization of Callovian “ Macrocephalites ’’ 
deposits has to yield to that of sequence opens up an interesting specula- 
tion — that the history of the earth, as told in its deposits, has occupied a 
far longer time than was formerly supposed. All recent work on Jurassic 
rocks leads to this result — that the postulate as to time required must 
certainly be multiplied by ten. The deposits and fauna of any one area 
during any specified period of time cannot be regarded as full evidence for 
the length of time required: this is only to be obtained by putting together 
and comparing results from all known areas. Even then there must 
remain many unknown areas to add their quota. When these have been 
fully explored it is not certain that the full tale of past events has been 
discovered— much may have been utterly destroyed beyond the possibility 
of recall. Thus is reached a conclusion that these palaeontological studies 
give evidence for greatly increasing the time-estimate for the earth's 
history and yet that such increase based only on present knowledge may be 
greatly understated. 
BIBLIOGRAPHY 
The following is a list of the works cited. Many more works professing 
to figure Ammonites macrocephalus or Macrocephalites have been consulted: 
in many cases the forms have little or no connexion with Macrocephalitidae, 
or are to be excluded as not comparable with the Canadian shells. Lemoine 
cites, up to 1911, some eighty names of species, but shows, by the generic 
names which he appends, that many are to be excluded from Macro- 
cephalitidae. 
Baier: Monmn. petrif. orcytographiae noricae, supplement!, 1757. 
Blake, J. F.: Fauna of the Cornbrash (Pal. Soc.) 1905-1907. 
Buckman, S. S.: 
(1) Kelloway Rock, Quart. Jour. Geol. Soc. LXIX, 1913, p. 152. 
(2) Yorkshire Type Ammonites, II, 1913-1919. 
(3) Type Ammonites, III, 1919-1921. 
