40 



anccps, tvig'onia (lcodal;«a, T. carinafa, rhynchonolla 

 Rihbsiana, tcrebratula sella, and large species of cephalopods, 

 belonging to the genera — nantilus, ammonites, ancyloceras, 

 and also bclomnites ; the latter form is allied to the cuttle- 

 fish of our present seas. 



THE GABLT. 



Proceeding alorg the Faversham road over Kennington 

 Common, we amve at Leneker Street, where we meet with 

 the gault. Gault is a provincial name for any bluish tena- 

 cious clay; but it has been adopted by geologists 

 to denote this peculiar clay, which contains 

 indurated argillaceous concretions and layers of 

 grcensand- In the bottom bed phosphatic nodules are 

 found at "West well Leacon, at Folkestone, and near Farn- 

 ham in Surrey they are so abundant that they arc ground 

 down and used as a manure on account of their containing a 

 large percentage of phosphate of lime, of animal origin, partly 

 coprolitic, propably derived from the excrements of fish. 

 The gault is described as having an average of 100 feet, but 

 I have not met with it beyond 45 feet in thickness. This 

 bleuish clay presents no disttnctive mineral aspect, but is 

 rich in peculiar fossils, in excellent preservation, often with 

 their nacreous shells entire. 



UPPER GREENSAND AND CHALK MARL. 



The upper greensand seems in this district to have 

 become so mixed up with the chalk-marl as to be lost as a 

 separate stratum ; but in the Isle of Wight and some other 

 districts it is found to consist of green-sand with layers and 

 concretions of chert, and with seams and nodules of coarse 

 chalcedony. The chalk-marl is an argillaceous limestone, 

 and is so intimately connected with the upper grocnsand, 

 on which it reposes, as to be scarcely distinguishable 

 by an unpractised observer ; but it abounds in fossils 

 and contains numerous species of Ammonites and 

 other cephalopoda, which are either of excessive rarity in or 

 altogether absent from the upper chalk strata. Ammonites 

 varians, and A. MantcUi, are characteristic species of 



