BENSTED — OT^" THE GEOLOGY OP MAIDSTONE. 



447 



are obscurely marked by a few longitudinal ribs. The beak is somewhat produced, in- 

 curved, and truncated by a small foraniinal aperture, which is separated to some extent 

 from the hinge-line by a dcltidium. 'I'hc dorsal valve is not nearly as convex as the ven- 

 tral one, and is likewise divided into three portions, the central one being flattened and 

 furrowed by four longitudinal ribs, while the lateral portions become more elevated as 

 they approach the front, and curve inwards so as to meet the valve-edges of the central 

 lower portion of the valve. 



Upon each of the lateral portions of the valve may be observed six or seven ribs, which 

 become somewhat obscured as they approach the margin of the shell. Interior un- 

 known. 



Length, 1 inch 7 Hues ; width, 1 inch 3 lines ; depth, 10 lines. Tertiary, Malta. 



Ols. The recent species to which this shell bears the closest re- 

 semblance is the Waldheimiajlavescens, Lamarck, now alive in myriads 

 at Port Jackson, Australia, as well as in some other localities. The 

 recent species is however more regularly ovate than is the fossil one, 

 the beak is less elongated, and with a larger foraminal aperture. 



THE GEOLOGY OE MAIDSTONE. 



By W. H. Bensted, Esq. 



{Concluded from pa^e 382.) 



There only remains now to notice the post-Tertiary deposits to com- 

 plete this account of tlie geology of Maidstone. The surface-soil 

 and the earth filling in and covering over Ihe faults and large fissures 

 consist of clay, gravel, " sharp " drift-sand, and fine sand, all being 

 sedimentary deposits from water under difi'erent rates of motion. 

 The exteriors of the highest masses of rock show the effects of a 

 powerful erosion continued for a long period of time ; but this action 

 was not the dashing of billows, for some surfaces of the rock, although 

 worn to a great extent, have portions of fragile shells standing out 

 from their surfaces, just as in the cavernous gutters of the rock 

 masses of spiculae jut out from the walls, the loose sand or soft hassock 

 having been washed away. 



Old watercourses exist at a considerable 

 depth from the surface, showing that a gra- 

 dual lowering of the water-level of the springs 

 has taken place. 



The opinion I have formed respecting the 

 beds of drift and sedimentary clays, which 

 in the district are found between the masses 

 'Fig. 9. — Protrusion of Kag- of rock, is that an elevating force has lifted 

 stone into Drift, a^ INlaid- these masses, bearing up the drift and clay 

 stone. beds of Kagstone ; 9), and that, in some instances, the 



' peaks of the smaller masses of rock have 

 been protruded into the drift and elay, 

 piercing and dividing them into lines at angles parallel with their 

 sides. 



b b, drift ; c cc c, clay 

 line of Hints. 



