Inverted Mass of U'pper Cretaceous Strata. Ill 



present location, where tlie outlier at that time was capped by the 

 basal Cenomanian bed, or by remnants of it. 



(10) Thin ironstone-bands which form a conspicuous feature 

 in the section at Harris's Pit are developed principally along surfaces 

 of stratigraphical discontinuity. Their disposition within the strata 

 of both the normal and the inverted parts of the sequence shows 

 that they were formed by mineral segregation subsequently to the 

 glaciation. 



The present study emphasizes a lesson. Since the whole fabric 

 of stratigraphy is built upon the determination of age-relationships 

 among superimposed deposits, it follows that an essential of sound 

 stratigraphical work lies in the full utilization of all available 

 palaeontological criteria. If these be neglected, the data for correct 

 conclusions are incom23lete, and the investigator may thus perixiit 

 himself to be deceived by the apparent simj)licity of a stratified 

 series. The stratigrapher is too often dismayed by the complexities 

 of palaeontological classification and nomenclature ; but the 

 determination of the age of successive strata does not necessarily 

 demand an excursion into this forbidding domain. It can usually 

 be compassed without the naming of species. Nevertheless, some 

 knowledge of the faunal characterization of zones, as well as 

 familiarity with the principles underlying the right application of 

 that knowledge, must always form part of the indispensable 

 equipment for stratigraphical work. The trouble involved in the 

 use of these means for age-determination, however irksome it may 

 seem, can no more be evaded than that which' niust necessarily 

 be taken in the study of lithological characters and relations, from 

 which are deduced the conditions under which sedimentation has 

 taken place. 



In the case of a composite fossil fauna consisting of derived and 

 indigenous elements, the criterion of age is to be sought among 

 the zonally latest life-forms and not among the earlier ones. The 

 determination of age is then based ujoon previous experience of 

 uniformities, both as regards biological facies and zonal restriction. 

 Its accuracy is thus directly proportionate to the known in- 

 variability of the faunal and chronological inter-relation. 



The elementary truths embodied in these remarks have been 

 brought home to us by many workers since the days of William 

 Smith ; in more recent years by the illuminating researches of 

 Charles Lapworth, S. S. Buckman, A. W. Rowe, and other 

 investigators ; but there is perhaps no illustration of them more 

 convincing than that afforded by the study of Shenley Hill. 



Finally, we desire to express our indebtedness to those who have 

 kindly given help in the present investigation ; to Mr. Gregory 

 Harris and Mr. George Garside, who permitted us to visit their 

 sand-pits ; to Mr. Henry Woods for a list of fossils in the J. F. 



