362 J^^of. Sedgwick on the [May, 



notice the manner in which it is brought forward, we reply, that 

 the order of superposition cannot be determined against the 

 direct evidence of sections. If it can be shown that the section 

 given in the Geological Transactions * is erroneous, the argu- 

 ment may then be listened to, but not till then. Again, fresh- 

 water shells may be expected to appear occasionally in any bed 

 of a tertiary deposit. They exist hi great abundance in some 

 parts of the plastic clai/ formationy^f between the calcaire grassier 

 and the chalk of the Paris basin. Their existence in the sand 

 and plastic clay of the London basin only establishes a new ana- 

 logy between the contemporaneous forntations of the two coun- 

 tries. 



The observation on the Suffolk crag is given with too much 

 confidence. Some of the masses of broken shells might have 

 originated in the diluvian action which formed our great beds of 

 gravel. But in other places the shells make an approach to a 

 more regular arrangement, and are often associated with thick • 

 beds of siliceous sand. The coast of Essex may, perhaps, give a 

 clew to the true relations of the deposit. At all events we think 

 that even the imperfect denudations of the Suffolk coast prove 

 that the crag is superior to the Loudon clay. In the absence of 

 more perfect details, I will transcribe two important sections 

 which I obtained from my lamented friend Dr. E. D. Clarke. 

 They are made out from a register of the borings of the strata 

 undertaken last year in the hopes of finding a spring of fresh-, 

 water for the town of Harwich.j: 



First Section in the Town of Harwich, 



Feet. In. 



(1.) Soil 3 



(2.) Sand, a strong spring of salt water. 17 



(3.) Blue clay 20 



(4.) Shingle and gravel 20 



(5.) Red coarse sand 7 



(6.) Coarse gravel . . » 4 



(7.) Coarse dark sand 6 



(8.) Clay green and red 1 2 



(9.) Green clay , 1 10 



(10.) Chalk . .' 28 



(1 1.) Chalk mixed with fine sand 9 



(12.) Chalk, grey from the mixture of dark sand ; seve- 

 ral flints and pieces of septaria 72 



(13.) Pure carbonate of Ume 176 



Making in all 276 feet of chalk when the work was abandoned^ 



■* Vol. iv. pi. 13. 



+ I have been informed by my friend IVf r. Underwood, of Paris, that many of the 

 French naturalists now consider the plastic clay as the lowest freshwater deposit of the 

 Paris basin. 



i Before these borings were undertaken, no chalk had evei been reached in the neigh-, 

 bourhood. 



