446 S. Sharp — On the Northampton Oolites. 



of hardness of tlie rocks in question should be exactly counter- 

 balanced by the time taken by the retreat of the sea, the existence 

 of which it would be very difficult to prove. I merely bring it 

 forward for what it may be worth, as an explanation which, if it 

 may not be the true one in the present case, yet may, I doubt not, 

 be applicable to others. 



5. Summary.— ^\\Q conclusions I have endeavoured to shadow 

 forth in this paper may be briefly summarized as follows : 



1. That with the exception of a central double range of mountains 

 of elevation, Western Brittany consists of two great northern and 

 southern plains of marine denudation. 



2. That the last time these plains were exposed to the action of 

 the sea, was in Upper (?) Miocene times. 



3. That the rivers of Finistere are identical with those which 

 flowed from the central dry-land into the Miocene sea. 



4. That the valleys at the bottoms of which these rivers run are 

 the result of their erosive action, aided by other subaerial agents. 



5. That the uniformity of depth and breadth at present displayed 

 by these valleys is due to the degree of hardness of the rocks in 

 this district, being in an order of succession directly inverse as the 

 time during which they were submerged beneath the middle Tertiary 

 sea, and exactly proportionate to that during which they have been 

 exposed to present subaerial influences.^ 



V. — Notes on the Northampton Oolites. 

 By Samuel Sharp, F.S.A., F.G.S., etc. 



ATTENTION having been drawn of late to the "Northampton 

 Sand " by the able papers of Mr. George Maw and Mr. Judd, 

 and by the discussions which arose upon them, and to the Oolitic 

 beds of Northamptonshire generally, by the too concentrated article 

 (so rich in information) by Professor Morris, in the Geological 

 Magazine for March, and by a letter from the Eev. P. B. Brodie 

 elicited thereby in the May number, I venture to offer the fol- 

 lowing provisional statement as to the Oolitic strata in the neigh- 

 bourhood of Northampton, and the order in which they occur, pur- 

 posing at some future time to write more fully upon them, to 

 enumerate the pal^ontological contents of each bed, and to en- 

 deavour to correlate the Northampton series with those occurring in 

 the more northerly parts of the county and around Stamford. 



The thickness of the beds respectively varies greatly. I have 

 stated the maximum thickness of each in feet : 



fl. White Limestone 25 feet. 



p + l'-^. I^lue and Grey Clay 15 „ 



X^yf <; 3. White Sand 12 „ 



uoute. j 4, A Series of very variable beds— more or less ferruginous 30 „ 



(^ [Place of the Stonesfield Slate, which is absent.] 

 f f . (0. Coarse Shelly Calcareous Oolite, with numerous Fossils 4 „ 



n r!""^ 6. Sandy Slate, with Fossils 3 „ 



Uoiite. I ^_ Ironstone Beds . . - - from 1 foot to 25 „ 



Upper Lias. 



1 Eead at the British Association Meeting at Exeter, in Section C, on Saturday, 

 the 21st August, 1869. 



