Reviews — Brydoiie s Glialk of Hants. 123 



course, satisfying the definition of a zone), but original standardiza- 

 tions of zones should be retained. Nor does it seem desirable that 

 any separate index-fossil should be invested with a denotation 

 differing from that already generally accepted. Mr. Brydone is 

 careful to define his terms, but it must be borne in mind that the 

 arbitrary limitation of zones by successive workers tends to produce 

 hopeless confusion in zonal nomenclature. And here it may be 

 observed that only on the assumption that the boundaries of the 

 author's zones differ from those given in previous publications on the 

 Chalk is the difference in coloration in the map to be recommended. 



One desirable feature of Mr. Brydone' s work is the employment 

 of a standard of values in referring to the occurrence of species by 

 such terms as 'abundant', 'frequent', 'scarce', and so forth. 

 Doubtless much ambiguity has from time to time been caused by the 

 mode in which chance records have been interpreted and used as 

 premises for more important generalizations. This attempt, therefore, 

 at. greater accuracy is to be welcomed. 



A consideration of the general structure of the area dealt with 

 occupies more than twelve pages ; but extended reference to this 

 section is obviously precluded here. In discussing his methods of 

 mapping the author acknowledges the helpfulness of the work of the 

 Survey in having traced the salient boundary-lines. One inherent 

 difficulty in the author's undertaking was the lack of sections 

 showing the complete thickness of zones. A brief but well-considered 

 description of the locality of each exposure is given in a list, which 

 groups the localities according to horizons, each exposure bearing 

 a number corresponding to one on the map — a scheme that has been 

 found advantageous in works with similar aims. For the reception 

 of records not included in Messrs. Griffith & Brydone's book 

 a supplementary table of fossils has been prepared. This table is 

 prefaced by observations of which some seem to call for comment ; 

 and the author has done good service in abstaining from the use of 

 specific names that have no definite meaning (e.g. Serpiila plana). 

 Mr. Brydone finds himself unable to see any justification for the 

 record of Micraster prceour^or as a separate species, a view that will 

 come as a surprise to many Chalk workers. Such a point, in our 

 present state of knowledge, must be a matter of opinion ; but the 

 fact remains that the group of M. prcBCursor as defined by Dr. Rowe 

 is found very acceptable by workers in other parts of tiie country. 



A chapter of palseontological notes is found at the end of the book. 

 Here three new varieties of Echinocorys scutatus (vars. elevatus, 

 tectiformis, and ductus) are described, each occurring at a definite 

 horizon. A sequence in the dominant shapes and sizes of Ojfaster 

 pilula has been traced ; and two new forms of Bourgueticrimis 

 ('forms 6 and 7'), both of stratiyjraphic value, placed on record. 

 The determination of these as auxiliary guides is extremely useful. 

 Some attention has been bestowed upon Sponges, descriptions being 

 furnished of four new species of Porosphcera and two of Retispinopora 

 (new genus = Spinopora partim). Plicatula hantonensis is also among 

 the new species described. 



