BENSTED — ON THE GEOLOGY OF MAIDSTONE. 



297 



was exhibited at the Geological Society's meeting, as that of a 

 marine saurian, the phalaugial digits not being articulated by convex 

 and concave surfaces, as in the terrestrial group, but by plane faces. 

 These were roughened, indicating ligamentous connection. 



Professor Owen then mentioned also the occurrence of vertebrae 

 of a large Plesiosaurus in this chalk ; the late Mr. Dixon, of Worthing, 

 having had three or four in juxtaposition, which are now in the British 

 Museum. He considered the specimen belonging to Mrs. Smith, of 

 Tunbridge "Wells, as probably referable to that genus. It also pre- 

 sented considerable resemblance to another extinct genus, the Plio- 

 saurus, but the bones were thicker and not so expanded at their 

 extremities. There was also another large saurian of the Cretaceous 

 epoch, the Mosascniriis ; but altliough fine remains of its teeth and 

 jaws had been discovered many years ago, no extremities had ever 

 been found. If the teeth of the Mosasaurus should be found in the 

 locality where Mrs. Smith's specimen was got, he thought it might 

 indicate that the paddle above referred to belonged to that genus. 



The Firestone is very little developed in this neighbourhood. The 

 only traces I have seen are thin beds, a few inches only in thickness, 

 at Snodland, near the church. Between there and Burham Church, 

 a bar of rock runs across the river ; it is never dry, and its obstruction 

 causes a considerable fall when the tide is low. 



The best section of the Gault is at a place called the Varnes, on the 

 banks of the Medway, near New Hythe. At low-water the lowest 

 beds are to be seen. The bank is about fifty feet above low-water. 

 Slips are frequently occurring from the eflects of the weather, and the 

 current of the river washing away the softer parts, when fossils 

 may be found in abundance. Thence the gault may be traced to 

 Folkestone on the one side, and into Sussex on the other, forming a 

 valley at the foot of the chalk-downs. Its usual colour is light blue 

 when dry, but of a very dark blue when wet. Some veins of red 

 ochreoiis clay marked with Fuci {F. Targonii) occur frequently. 



The gault forms a stiff soil, locally known as " black land," and its 

 outcrop generally appears as a marshy tract. From its tenacity 

 and its dipping under the chalk-strata, through the cracks and fissures 

 of which the water finds its way, it forms a subterranean reservoir 

 from the junction or lip of which the springs burst out. 



I would here say a few words on the spring-heads of the Maidstone, 

 district. These are nearly all si- 

 tuated in circular cavities in the 

 Lower Chalk, where it projects 

 over the Gault, and an interesting 

 phenomenon is observable in the 

 retrogression of the spring-head 

 into the chalk by its erosive action. 

 If we suppose the waters originally 

 burst out at the foot of the hill 

 B, fragments of chalk would be 

 carried away at that point, and as the sides grew higher the rim of 



VOL. V. 2 Q 



Fig. 3. — Spriug-head. 



