PLINTS IN CHALK. 77 



the flints in lines would be accounted for, supposing them 

 to have been formed on that sea-bottom, and the source from 

 which they have been derived is doubtless the petrifaction of 

 sponges, madrapores, &c., there formed. Dr. Carpenter (in 

 the work before referred to) says : " It may be stated, as a 

 fact beyond all question, that nodular flint and other 

 analogous concretions (such as agates) may generally be 

 considered as fossilised sponges or aicyonian zoophytes, since 

 not only are their external forms and their superficial 

 markings often highly characteristic of those organisms, but 

 when sections of them are made suificiently thin to be 

 transparent, a spongy texture may be most distinctly 

 recognised in their interior." 



During the deposition of these secondary strata in the 

 hollows of the surface, but little alteration of the relative 



FIG. 30. TEKTIAKY FORMATION. 



situations of sea and land could have taken place, as the 

 deposits for the most part lie conformably to the same 

 hollows or " basins " (fig. 30 will illustrate this) ; but after 

 the deposition of these strata, there appears to have been a 

 very great disturbance, many chains of mountains were 

 cast up (as the Apennines), carrying upwards with them 

 these deposits ; some of the strata were so displaced that 

 they were left in a perpendicular position, as may be seen in 

 several places at the south side of the Isle of Wight. These 

 disturbances, however, did not amount to so general a con- 

 vulsion as those before described, nor is it known whether 

 all the effects produced on these strata took place at or near 

 the same period of time ; they nevertheless appear to have 

 produced an almost total change in the situation of the land 

 and sea, for the " downs " of chalk (on the southern coast of 

 England, for example) were, before these changes, the beds 



