198 F. L. Kitchin & J. Pringle — The Uj>'per Gault in 



to have yielded no distinctive fossils. Our examination of the 

 reddened and mottled Chalk above satisfied us that the allocation 

 of those beds to the Lower Chalk by Hill and Jukes-Browne was 

 correct. 



IV. Concluding Remarks. 



In the foregoing notes we have endeavoured to bring into proper 

 relationship some of the main facts concerning the overlap of the 

 Upper Gault in England. The abundant evidence for this extension 

 of the sea-floor in the marginal regions of the area of deposition can 

 only be rightly understood if due attention be paid to the age- 

 determination of the basal part of the Gault exposed in the different 

 localities. When the available geological accounts of these rocks 

 published during recent years are examined, it is surprising to find 

 how often the true meaning of the facts has been overlooked. This 

 has too frequently been due to the neglect of fossils or to an imperfect 

 understanding of their significance. In fact, the broad methods of 

 geological cartography, divorced from accurate palaoontological 

 work, have been too much in evidence. In many cases it can only 

 be inferred from their writings that Jukes-Browne and other well- 

 knov/n geologists believed the Lower Gault to pass transgressively 

 over older beds, whereas, by closer examination of the strata, we 

 have found that it is in reality the Upper Gault. Professor Barrois 

 had clearer conceptions on this point ; and it is much to be regretted 

 that subsequent work was not more carefully built upon the 

 foundation of astute observation and deduction so well laid bv him 

 in 1876. 



We have followed this overlap m a direction where, to the west, 

 the facies of the deposits is traceable through the region of silty 

 and saiidy clays to a more purely sandy and shelly littoral develop- 

 ment. Again, in the south central counties we have found at times, 

 in the area of clay deposition, evidence of tranquil sedimentation 

 where moUuscan life soon found a bearable habitat on the newly 

 invaded ground ; or, again, abundant signs in the scarcity of fossils 

 and the brecciated character of the lowest clays that rapid 

 accumulation and turbid-water conditions had delayed these 

 adjustments. And, finally, in the eastern counties, we have seen 

 the approach to a region of much scantier, clearer-water calcareous 

 deposition, where there is a great condepsation of the strata. Our 

 observations at Grimston and Roy don are particularly significant 

 in this connexion. 



In tracing these developments, certain faunal constituents of the 

 lower part of the Upper Gault have been of great value, particularly 

 those that characterize Bed IX at Folkestone. These indicators 

 have led us to conclude that one general movement of depression 

 was responsible for the transgressive extension of the Gault strata 

 in this country. The interrujnus -Gawlt is found always to rest 

 upon the mammillatus-zone, and these beds have a much more 

 restricted lateral distribution than the Upper Gault. These 



