82 TOWN GEOLOGY. [HI. 



few found in the New Red sandstone, we have a righb 

 to call them another world, and that one which must 

 have lasted for ages. 



After we pass Oxford, or the Vale of Aylesbury, we 

 enter yet another world. We come to a bed of sand, 

 under which the freestones and their adjoining clays 

 dip to the south-east. This is called commonly the 

 lower Greensand, though it is not green, but rich iron- 

 red. Then succeeds a band of stiff blue clay, called 

 the Gault, and then another bed of sand, the upper 

 Greensand, which is more worthy of the name, for ifc 

 does carry, in most places, a band of green or "glau- 

 conite" sand. But it and the upper layers of the lower 

 Greensand also, are worth our attention; for we are all 

 probably eating them from time to time in the form of 

 bran. 



It had been long remarked that certain parts of 

 these beds carried admirable wheatland ; it had been 

 remarked, too, that the finest hop-lands those of 

 Farnham, for instance, and Tunbridge lay upon them: 

 but that the fertile band was very narrow ; that, as in 

 the Surrey Moors, vast sheets of the lower Greensand 

 were not worth cultivation. What caused the striking 

 difference ? 



My beloved friend and teacher, the late Dr. 

 Henslow, when Professor of Botany at Cambridge, had 

 brought to him by a farmer (so the story ran) a few 

 fossils. He saw, being somewhat of a geologist and 

 chemist, that they were not, as fossils usually are, 

 carbonate of lime, but phosphate of lime bone-earth. 

 He said at once, as by an inspiration, "You have 

 found a treasure not a gold-mine, indeed, but a food- 

 mine. This is bone-earth, which we are at our wits' 



