262 Rev. W. D. Conybeare on the Phenomena of Geology 



this ? Seeing that since the Romans occupied Eboracum 1 700 

 years ago, that agency has not effected a degradation of 

 7 inches on any one of the valla of their encampments, we 

 may perhaps have sufficient data to calculate upon. I leave 

 the Fluvialists to work out the question at leisure, offering in 

 the meanwhile, as a mere approximation, an infinitillion of 

 ages in the ?/th power. 



3. We next come to the breach of the river Witham, through 

 the oolitic range at Lincoln, where a dam of very trifling ele- 

 vation would at once turn it into the Trent. 



5. South of this the oolitic range is broken through by the 

 transverse valleys of the Welland and Nen : but as the head 

 waters of these streams rise almost within the limits of these 

 valleys, I shall not insist on them ; though as the breaches tra- 

 verse the whole chain, I do not see how the Fluvialist can ac- 

 count for them without filling up the subjacent plains on the 

 north-west as before. 



6. I now arrive at my old ground, the district containing 

 the Cherwell and other head waters of the Thames ; and 

 must refer to my former observations. 



7. The chalk range is broken through not only by the 

 Thames, but by a very considerable number of valleys, a 

 complete transverse valley occurring almost every 10 miles 

 throughout the course of that formation. Many of these valleys 

 afford a passage to actual streams; and many others, quite an 

 equal number I believe, are totally destitute of such rivers, 

 and yet bear every character of being truly valleys of excava- 

 tion. The chalk, indeed, as must be familiar to those who 

 have resided long in any district chiefly composed of it (the 

 locality of much of my own youth), abounds in valleys devoid 

 of water, the stratum being so absorbent as generally at once 

 to swallow up the atmospheric showers without allowing them 

 to collect into rills. Now I very earnestly wish that the Fluvi- 

 alists would inform me how tljese valleys, which neither have 

 nor ever have had streams flowing through them, have been 

 formed by the erosion of the said non-existing streams. 



8. The valleys of excavation at the south-western extremity 

 of our district, Dorset and Devon, have been fully described in 

 an essay by my friend Buckland in the Geological Transac- 

 tions, vol. v. ; and wherever he has preceded me, I am always 

 content with reference only. 



9. I will conclude therefore with the south-eastern extre- 

 mity, the Weald of Kent. It is well known that the axis and 

 saddle of this district consists of a range of sand denominated 

 (from the place where it terminates on the coast) the Hastings 

 Sand. Round this axis mantle the upper and ferruginous green 



sand 



