Reviews — Richardson s Geology of Cheltenham. 79 



■Secretary of the Cotteswold Naturalists' Field Club (as it is now- 

 termed), has given us the latest results of research in the fascinating 

 region of Cheltenham. "We may at once say that the work bears 

 abundant evidence of his knowledge, diligence, and enthusiasm. 

 He has brought together the available material that bears on the 

 geology, and especially on the life-history of the local rocks from 

 the Trias to the Forest Marble. We find consequently much 

 information on the horizons of fossils, as well as on the zones, 

 which, being based on paleeontological evidence, ai'e naturally inde- 

 pendent of the ordinary limits of geological formations. The 

 term zone is used to imply the deposits (of whatever character) of 

 a particular period of time ; while the term hemera is used to 

 denote the time of a zone. As defined by Mr. Buckman the 

 hemera is " the time during which a particular species — generally 

 in Mesozoic chronology, of an ammonite — has dominant existence." 

 With his aid the author enumerates 29 hemeree for the Liassic 

 series and 16 for the Inferior Oolite series. We should agree, 

 however, witli Mr. Hudleston in maintaining " the chronological 

 value of Ammonite zones," and we prefer to consider the hemeraa 

 a,8 minor adjuncts of zones. ^ 



It is evident that to follow the author much preliminary know- 

 ledge will be required. His work is an advanced rather than an 

 introductory guide, and it appeals much more to the specialist than 

 did any of the handbooks previously published. Thus, in describing 

 the zone of Schlotheimia angidata (p. 40), he observes that "Beds 

 usually referred to this zone have been found to have accumulated 

 during two hemeras — the hemeras megastomatos and marmorece." 

 We fail to find any explanation of these two hemeree. Thei'e are 

 many other hard nuts for the student to crack, if he be not specially 

 instructed in the vicissitudes of paleeontological nomenclature. No 

 doubt the most difficult part of the author's work has been to 

 employ the latest names assigned to the species he mentions. 

 Thus Ammonites rnricostatus (after three or four intermediate names) 

 is now Echioceras raricostatum. The Opaliniim-zone is duly noted, 

 but we are by no means sure that any fossil corresponding to 

 Ammonites opalimis is now recognized in the district, although 

 included in the Opalinum-zone are the " Opaliniforme-heds " with 

 Ci/pholioceras ojyaJiniforme. 



Here we may remark that we do not like the vague name 

 '• pre-planorbis beds," introduced by the author for the Ostrea-heds 

 at the base of the Lower Lias. He finds fault with the term 

 ^•' White Lias," but it is a useful stratigraphical term for the Upper 

 Rhaetic beds in the region extending southwards from Bath. 



The fact that zonal divisions often transgress the limits of 

 ordinary stratigraphical divisions leads the author to speak of 

 a "new school of geologists" who give "names to the time during 

 which the beds were deposited," in contrast to an " old school of 

 geologists" who placed "too much reliance upon lithic structure." 



1 See discussion in Geol. Mag. for 1902, p. 554; 1903, pp. 36, 95, 141. 



