328 Mr. R. C. Taylor on the Geological Features 



But I have nowhere asserted that the exuviae are uni- 

 formly continuous, or even that the beds which contain them 

 are wholly so. On the contrary, those inferences are ex- 

 pressly guarded against, when remarking that a leading charac- 

 teristic of the shells is, " that they are by no means diffused in 

 equal numbers and projiortions, but occur, at intervals, in 

 groups and genera ;" and that wherever the chalk or earlier 

 formations rise above the general level of the crag, that de- 

 posit would then be absent, — circumstances which find a pa- 

 rallel in all the soft strata above the chalk, from the plastic 

 clay upwards. It was further observed, that the upper marine 

 deposits in some cases appear to surround the bases of chalk 

 eminences, which then " present the appearances of tongues 

 or promontories, protruding into the crag" district, and "ac- 

 count for the occasionally apparent absence of that formation," 

 and for the sinuosities of its outline. This is also of common 

 occurrence in the later deposits, whose boundaries are much, 

 but not entirely, influenced by the configuration of their chalk 

 basis. 



That the organic remains, peculiar to certain strata, are 

 sometimes unusually abundant and sometimes absent from 

 their matrices for considerable intervals, we might appeal to 

 the experience of every practical geologist, who has traced in 

 detail any of our superior formations, such as the plastic and 

 London clays, and indeed, some of the indurated strata, such 

 as the lias, (lyers?) the oolites, and the calcareous sandstones. 

 Yet the identity of these strata is in most cases satisfactorily 

 established. So also with the crag beds, which may be fre- 

 quently seen in the open face of a cliff or excavation, in parts 

 abounding with fossil shells, in others devoid of them : some- 

 times suddenly ceasing; sometimes gradually thinning off; 

 but the continuity of the matrix is still apparent and unques- 

 tionable. Perhaps there is no formation in the entire range 

 of superior and supermedial strata, whose organic accompani- 

 ments are not unequally distributed, and at times wholly in- 

 terrupted. 



I am perfectly aware, from personal experience, how well 

 this observation applies to the deposits in East Norfolk, and 

 how often the sand and gravel beds are either without fossils, 

 or contain only occasional indications of their existence. But 

 enough has been seen to prove that the lower beds on which 

 the diluvium and " the ante-human gravel " repose, may be 

 classed with the highest known marine formations. 



In most of the instances whei'e the ci'ag is exposed in the 

 Norwich valley, the chalk hills rise higher than the shelly beds, 



and, 



