4 
of Hazelton district have been pointed out by both Hanson 1 and the 
writer. 2 There, too, in the Hazelton series, the fossiliferous basal Middle 
Jurassic rocks are followed by massive accumulations of tuff, agglomerate, 
etc., probably also of Middle Jurassic age, and pointing as at Skidegate 
inlet, to intense volcanic activity. The uppermost part of the Hazelton 
series, the upper sedimentary division of Hanson, is without volcanic 
material, but as these rocks are unfossiiiferous the date of the cessation of 
volcanic activity in this area cannot be determined, although it may also 
be Upper Jurassic. Extension of studies of this kind should result in the 
dating of times of volcanic activity and in the locating of the sites of volcanic 
activity and deposition, and thus form an important contribution to the 
study of the igneous geology of the Canadian Cordillera. Other applica- 
tions of the fossils are the dating of igneous intrusions, etc. Thus the 
study of the Mesozoic fossils of western Canada becomes, not an end in 
itself, but a means to an end, the solution of the history of the Canadian 
Cordillera. 
In the succeeding account, measurements of the ammonoids are given 
as follows, and in the following order: diameter of specimen in millimetres 
and height of whorl, thickness of whorl, and width of umbilicus in per- 
centages of the diameter. Although no graphs of shell proportions are 
figured they have been prepared and are made use of in descriptions of 
genera and species. The following symbols are used: ES for external 
saddle, SI for first lateral saddle, S2 for second lateral saddle* EL for 
external lobe, Ll for first lateral lobe, L2 for second lateral lobe, aux. for 
auxiliary lobe, etc. Lower, Middle, and Upper Jurassic are used as pro- 
visionally defined in a previous paper. 3 Except where otherwise stated all 
illustrations are natural size. Ammonoid specimens are not abundant, so 
that variation and intergradation cannot be studied. 
JURASSIC AMMON 01 DE A 
Phylum, MOLLUSCA 
Class, CEPHALOPODA 
Order, Ammonoidea 
Family, Gowericeratidae S. Buckman 
Genus, Seymourites Kilian and Reboul 
1909. Seymourites Kilian and Reboul, Wissenschaftliche Ergebnisse der 
Sehwedischen Sud-polar Exped. Band 3, Lief 6, p. 26. 
1927. Yakounites McLearn 4 , Trans. Roy. Soc., Canada, 3rd ser., vol. 21, 
sec. IV, p. 71. 
At the stage of growth of the anterior part of the penultimate and the 
posterior part of the ultimate whorl the shell is subangustumbilicate, and 
about sphaeroconic, with somewhat convergent sides, but broad venter. 
On the ultimate whorl there is umbilical enlargement and eccentrumbili- 
cation; whorl contraction in anterior part of ultimate whorl. Inner whorls 
1 Geol. Surv., Canada, Sum. Rept. 1925, pt. A, p. 107 (1926), 
5 Trans. Roy. Soc,, Canada, 3rd ser., vol, 21, p. 65 (1927). 
* Trans. Roy. Soc., Canada, 3rd ser., vol. 21, sec. IV, p. 62 (1927). 
4 The generic name Seymourites was at first overlooked because of its publication in a work on Cretaceous 
ammonites. No adequate description of Seymourites was given by Kilian and Reboul and its true systematic 
position was unknown to them. They considered it a subgenus of Kossmaticeras, It is unlikely that the Snowhill 
specimen figured by Kilian and Reboul can be referred to Whiteaves’ species or to the family Gowericeratidae. 
