498 J. Starkie Gardner — lielat ice Ages of 



proposed by Mr. Wallace, that Chalk is decomposed coral mud, could 

 not have been advanced by a geologist, as, while the Chalk contains 

 some well-preserved solitary corals, no remains Avhatever of reef- 

 building corals have either been found in or surrounding it, or even 

 in any deposit at all contemporaneous with it. I have dwelt at 

 some length on this point, as it is essential to remove such a funda- 

 mental misunderstanding before we are able to trace out the relation 

 between the Cretaceous and Eocene series of deposits in Europe. 



The whole Cretaceous series, in at least its typical area, is 

 evidently the gigantic result of a gradual encroachment of sea over 

 a former land. The process commenced with the Neocomian, when 

 the East of England was submerged, except the Palaeozoic ridge 

 which now passes under London. The incursion was checked until 

 a far more serious and sustained depression of the land and adjacent 

 sea-bed led to the formation of the Gault and Upper Greensands. 

 The downward tendency was steadily maintained until the end of 

 the Clialk age, when some undiscovered cause checked and reversed 

 the movement, and led finally to the reappearance of the deep-sea 

 bed as dry land. The encroaching ocean was probably, in part, the 

 j)resent Atlantic, and the depression seems to have slowly travelled 

 froni the English Channel in an easterly direction across Central 

 Europe, forming a gulf of constantly increasing magnitude. As the 

 land subsided and became sea. Blue and Green muds were thrown 

 down, to be succeeded in due time by Chalky ooze. It would be 

 physically impossible for the latter, supposing it to represent Globi- 

 gerina ooze, to be directly formed on a former land surface, and 

 we thus invariably find true Chalk preceded by some more littoral 

 quality of sediment. The nearer the original centre of depression 

 and focus of the subsidence, the older must be the Upper Green- 

 sand or Gault ; and the farther we recede from it in any landward 

 direction, the newer it must be. The littoral zone would have been 

 constantly travelling outwards and forwards, occupying the sea-bed, 

 until the ever-increasing depth led to a change in the sediment. 

 Thus, though we have perfectly continuous beds of Greensand, of 

 precisely the same lithological character, and extending over large 

 aieas, it would be rash in the extreme to assert that portions of it, 

 separated by one or more degrees of latitude and longitude, are 

 synclircnous. So with the numerous zones into which the Chalk 

 has been divided by Dr. Charles Barrels, and which, from their 

 regular sequence of superposition, must indicate variations in the 

 nature of the ooze, resulting from the continued deepening of the 

 water. The Chalk with flints of one locality would be deposited 

 synchronously with the Chalk without of another, and this in turn 

 with the Chloritic marl of another and the Greensand of another. 

 The zone of Greensand would travel forward as long as the sea 

 continued to encroach, and towards its extreme confines would 

 recede again when elevation set in, without any Chalk having been 

 deposited on it, so that a part of the Greensand may be actually 

 newer than almost the whole of he Chalk. It is probable that 

 each minor zone of depth, with itstslightly different quality of sea- 



