BENSTED — ON THE GEOliOGY OF MAIDSTONE. 
297 
was exhibited at the Geological Society's meeting, as that of a 
marine saurian, the phalangial 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 abo 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 resemblaiice 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 Mosasaurus ; 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. Thc- 
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 tlie other, forming a 
valley at the foot of the chalk-downs. Its usual colour is liglit blue 
when dry, but of a very dark blue when wet. Some veins of red 
ochreous clay marked with Euci {F. Targonii) occur frequently. 
The gault forms a stiif 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, fragjuents of chalk would be Fig. 3.— Spring-head, 
carried away at that point, and as the sides grew higher the rim of 
VOL. V. 2 Q 
