Inverted Mass of Uj^per Cretaceous Strata. 15 



From the above observations it is seen that no part of the Gault 

 in this pit can be placed lower than the rostratus beds. The character 

 and distribution of the fossils lead us to conclude that the upper 

 part of the clay belongs to a lower zonal level than the lower part. 

 Elsewhere Inoceramus sulcatus and ScJiloenhacMa varicosa are 

 common in the lower part of the rostratus beds, absent in the higher 

 part. At Harris's Pit these relations are reversed. If the absence 

 of these fossils from the lower beds there might be thought to 

 indicate that these strata rej^resent the Lower Gault, this is contra- 

 dicted by the positive evidence of the fossils present and by the 

 absence of any characteristic Lower Gault species. Bearing in mind 

 that the brachiopod-bed, which here underlies the Gault, contains 

 a fauna characteristic of a still later geological date, the facts already 

 set forth seem explicable only on the assumption that the series 

 here exposed is in an inverted position. 



It must be noted that the zonally highest Gault seen in this section, 

 that is to say the lowest part of the inverted mass of Gault, is not 

 of sufficiently late age to be succeeded immediately by the basal 

 bed of the Cenomanian stage in a series where there is no zonal 

 break. There is evidently a chronological gap and stratal non- 

 sequence of some magnitude between the clay and the brachiopod- 

 limestone of bed D. The bed of green sand sometimes intercalated 

 between these strata, once seen by Mr. LamjDlugh in the contiguous 

 Garside's Pit, provides evidence of the former existence of the 

 connecting deposits. Its faunal and lithological characters, as well 

 as its position, can leave little doubt in our minds that it belongs_ 

 to the zone of Pecten asper, which may have had ample representation 

 here prior to the period of erosion marked by the basal Cenomanian 

 bed. We have never had the good fortune to see any of this green- 

 sand in the present section. It ajopears, however, to have been met 

 with many years ago in Harris's Pit, when the working-face was 

 situated farther to the east, as well as in Garside's Pit, where it 

 was laid bare between the years 1904 and 1906. The junction between 

 the Gault Clay and the intermediate remnant of the Upper Green- 

 sand may itself form a line of earlier non-sequence than that shown 

 by the direct contact between the clay and the basal Cenomanian 

 bed. On this point, however, there is at present no conclusive 

 evidence. The facts as we have sketched them provide a simple 

 explanation of the relations between Gault and basal Cenomanian 

 in this section, and one which is wholly in accord with the established 

 principles of zonal determination and correlation. We shall now 

 show that this reading of the evidence obtained at Harris's Pit 

 is amply supported by a comparison with other sections. 



(To be continued.) 



