206 Dr. W. B. Clarke on the Crag of Suffolk. 



Pliocene Group. 



Red Crag of England : Subapennine Hills ; containing from 35 

 to 50 per cent, of recent species. 



Pleistocene Group. 



Mammaliferous Crag of England : Sicilian deposits ; containing 

 from 90 to 95 per cent, of recent species. 



Since the publication of these characteristics of the Crag, ex- 

 tensive excavations have been made within it in several localities 

 between the rivers Orwell and Deben, and on the banks of the 

 latter, in which many interesting discoveries have been made in 

 the organic remains of the deposit. 



The above-mentioned excavations have shown that above the 

 London clay and beneath the Red Crag, extending over certain 

 spaces, a bed is found varying in thickness from 3 or 4 inches 

 to about a foot and a half, consisting of fragments of bone, 

 usually of flattened form, with their ends and edges rounded by 

 attrition, interspersed amongst numerous irregularly-formed, 

 more or less rounded nodules, which appear to be indurated 

 clay : some of these latter exhibit an irregular cleavage in angu- 

 lar fragments, the inner surfaces of which show the presence and 

 infiltration of phosphates and carbonates of iron. Amongst these 

 are found others exhibiting a concentric structure, exposing and 

 disintegrating the contiguous layers of which the nodule con- 

 sists. Some of these appear to owe their origin to a nucleus of 

 oi-ganic matter, as a vertebra, a tooth, a shell, a small branch of 

 wood, or some other substance around which the argillaceous 

 layers have accumulated. Others exhibit a minute structure 

 corresponding in character with the usual appearance of septaria 

 from the London clay, having the interstices of the clay filled 

 with carbonate of lime frequently tinged by phosphate of iron. 

 These nodules not only abound in the stratum beneath the Red 

 Crag, but are also dispersed in various directions throughout the 

 general mass without any disposition to stratification, showing 

 they have been deposited promiscuously during the whole of the 

 Red Crag period, or whilst that deposit was being formed. 



Again, we find arenaceous clay nodules that have been rounded 

 by attrition into forms more or less spherical, upon breaking 

 which a shell, frequently a bivalve, is found in the interior, 

 having served as a nucleus around which the argillaceous sub- 

 stance has consolidated : in some instances the shell itself is 

 found ; in others nothing but the cast of it remains. It is not 

 unlikely that the presence of the shell and its molluscous inha- 

 bitant involving certain chemical changes within the mass of clav 



