1868.] HUGUES HERTFORDSHIRE GRAVELS. 287 



3rd. A period of submergence, when most of the old valley-deposits 

 were re-sorted, and Boulder-clay deposited under, in, and on them. 



This submergence went on until the Boulder-clay was dropped on 

 the sides of the hills, and even on the top of the Higher Plain. 



4th. A period of emergence, during which the present valleys were 

 scooped out of the Lower Plain. 



7. Conclusion. — The explanation I offer of the phenomena implies 

 periods of submergence and emergence and periods of subaerial and 

 fluviatile conditions so vast, that we may expect to find deposits of 

 intermediate age, the record of various intermediate conditions. 



Some such explanation must be given of the nearly obsolete ter- 

 races of gravel at the north end of Essenden Hill, some way above 

 the Lower or Valley-Plain ; also in Hatfield Park, south of the 

 house ; but I have no good evidence to off'er as to their exact posi- 

 tion in the series. Nor can I show where to place the pebble -gravel 

 associated with brown clay in pipes and patches north of St. AlLans. I 

 do not think it can be referred to the Upper-Plain Gravel ; but it may 

 be the result of the subaerial waste of pebble-bearing Tertiaries (fee. 

 The manner in which the gravel and brown clay sometimes seem 

 kneaded up together is curious, and can hardly be referred entirely 

 to their sinking into pipes. 



I do not off'er this as an exhaustive sketch of the Posttertiary 

 deposits of the neighbourhood of Hertford. All I mean to say is, 

 that these are true natural divisions, which it is well to establish in 

 a district where their relations to one another are more clearly seen, 

 before any attempt be made to correlate them with similar dej)osits in 

 other localities. 



Postscript. — Since this paper was written, I have procured some 

 mammalian bones from the gravels of the Lower Plain at Camps-HiU 

 brickfield, near Hertford, some of which I saw in place. They are 

 mostly in a very fragmentary condition ; but Mr. Boyd Dawkins has 

 referred them to Horse, Ox, Reindeer, Mammoth, and Tichorhine 

 Rhinoceros. Through the kindness of Mr. Andrews, of the Camps- 

 Hill brickfield, these are now in the Jermyn- Street Museum. 



The section (fig. 2) shows the position of the bones. 



Fig. 2. — /Section in Camps-Hill Brickfield. 



Scale, 8 feet to 1 inch. 



A. Newer brick-earth, a buff or yellow-brown loam, with about 18 inches of 

 irregular fine flint-gravel in base. 



B. Sand and loam, with Mammalian remains. t Position of bones. 



