XX. 



Under the term Upper Crag, will be described all the beds which 

 intervene between the Coralline crag and the glacial deposits, which 

 have been sub-divided into Red crag, Fluviomarine crag, and Chilles- 

 iord beds, there being no evidence of distinct succession, though the 

 latter beds are distinctly more recent than part of the former ; but there 

 :are reasons for supposing that the whole of these beds were deposited 

 upon, or near, some shore in a comparatively short period of time, 

 during which the sea was getting gradually more shallow. Certain it is 

 that the fossils found in the upper beds denote a climate gradually 

 becoming colder, and that the water was becoming brackish, and that 

 :an estuarine condition obtained ; and perhaps locally the terms might 

 be of use in denoting altering conditions ; yet, if retained, they would 

 seem to point out that these beds followed each other in distinct up- 

 ward succession, and were not contemporaneous in any degree. 



The Upper crag is found- lying immediately above the Coralline; 

 "but where the latter is absent, it rests upon the London clay. It occu- 

 pies a much more extensive area than the older crag, extending into 

 Essex as far as Walton on the Naze Eastward ; outliers are found at 

 Sudbury, resting upon the Thanet sands ; and deposits which are doubt- 

 fully referred to this formation, are found near Bardwell, Stanton. and 

 in the Gipping valley Northwards and this is the portion which has 

 been named the Fluviomarine crag. The deposit extends nearly up to 

 the City of Norwich ; this portion shewing from its fossils that it was 

 deposited under a colder climate, and in shallower water (estuarine), 

 than the portion further South. 



The crag consists of beds of ferruginous sand and shelly debris, 

 containing in places vast quantities of perfect shells, inclined at various 

 angles. The whole series is between 30 and 40 feet in thickness. 

 Where the crag is far below the surface, it is found to be of a blue colour, 

 containing the iron as a protosalt ; but most commonly it is red, due to 

 the oxidation of that metal. In places no traces of shells are to be 

 found, these having been removed by decalcification ; elsewhere, casts 

 ' are common, due to the deposit of iron oxide around them previous to 

 decalcification. The beds are highly fossiliferous 92 per cent, of the 

 fossil mollusca belonging to still living species ; and several species of 

 corals, cirripedee, echinodermata and polyzoa, a good percentage of 

 "which belong to still living forms, are also to be obtained, together 



