PLIOCENE PERIOD IK EITGLAND. 497 



in this trough, applied to the phenomena disclosed by the Yare 

 valley, clears np, it seems to me, all difficulty, and proves that 

 the Hoxne palaeolithic brickearth, so well known to geologists by 

 the description of Prof. Prestwich, is of the age of the Chalky 

 Clay itself, though of the latest part of it. 



The sections of Mr. Prestwich* show clearly that this brick- 

 earth could not have accumulated while the Waveney valley was in 

 its present state. It must have been formed either before the valley 

 was excavated through the Chalky Clay or when, after having 

 been formed, it was filled up again. Mr. Prestwich (unaware, I 

 presume, of the position which I have described as occupied by 

 the Chalky Clay in the valley bottoms) adopted the first alternative ; 

 and he attributed the patches of gravel, which extend along the 

 upper edges or brows of this valley for several miles in this part, 

 to the deposit of the Waveney when it flowed over the Chalky 

 Clay at this high level, and before it had excavated its valley. 

 To this period and to this condition of things, as I understand 

 his memoir, he refers the Hoxne brickearth, which has been de- 

 nuded on one side by the formation of the valley of the Goldbrook, 

 a stream flowing into the Waveney hard by. 



The lateral valley of the Goldbrook, thus on one side excavated 

 out of the palaeolithic brickearth, must no doubt be, if not wholly, 

 at any rate partially, of posterior formation to this brickearth ; but 

 such is, I think, clearly not the case with the valley of the Waveney; 

 and the explanation which I ofl'er of it, and which appears to me 

 quite sufficient, is tha,t when the ice of the Chalky Clay, shrink- 

 ing into these valleys and creeping through them, ploughed-out 

 the long trough in which the Little Ouse and Waveney now run, 

 it fllled this up, so that the drainage produced from the thawing 

 during summer of the land- surface (and which surface, the ice 

 having shrunk from it, had become covered with vegetation), 

 not being able to escape into the valley, formed a lagoon there — 

 a " Marjelen See " in fact ; and that this drainage, collecting what 

 debris there was scattered over the land-surface and swept by the 

 melting snows, carried it into the lagoon. In this way the imple- 

 ments of man and the remains of land and freshwater organisms 

 described by Mr. Prestwich were introduced into the brickearth. 



The connexion of the thin envelope of sandy gravel, which Mr. Prest- 

 wich shows as wrapping the denuded surface of this brickearth, I 

 defer for consideration in Stage lY., its connexion being with the 

 melting of the ice in West Norfolk, and with the sand and gravel 

 resulting from this, which are described in reference to that stage. 



All the East-Anglian valleys exhibit this plunging behaviour of 

 the clay — -that of the Blackwater being illustrated by fig. YII., and 

 that of the Gipping by figs. I. and I. a. Both of these valleys pre- 

 senting this feature at the point where the laying down of the 

 Chalky Clay upon c by the precession of the mud bank became 

 arrested, they furnish important evidence of the change in the mode 

 of ice-action which occurred towards the close of the formation, 

 ^ Phil. Trans. 1860, p. 304. 



