298 



THE GEOLOGIST. 



the hole would expand upon the surface, and thus a rounded cavity 

 would be formed, at the bottom of which the spring is now seen to 

 issue (at A). 



The water of these chalk springs is highly charged with calcareous 

 matter, obtained in flowing through the chalk fissures, and this is 

 precipitated on the fragments of sticks, roots, and leaves, which fall 

 into the streams. At Boxley Abbey very fine specimens of calcareous 

 tufa may be procured, as may be also incrustations of fir-cones, etc., 

 by placing them in the water near the spring-head. 



A spring of water at Cosiugton, bursting from the Lower Chalk, 

 deposits a coating upon the stones in its course of a bright crimson, 

 which at one time was considered to proceed from an impregnation 

 of iron-pyrites, but has now been determined to be of vegetable origin. 



The fossils of the Grault most common are Ammonites, Hamites, and 

 Inocerami. At the Yarnes great quantities of round nodular masses 

 are found. On breaking these stones a nucleus with concentric 

 waving lines is seen ; they take a polish without difiiculty. These 

 nodules, so rich in phosphate of lime, have been conjectured to 

 be coprolitic, but my opinion has long been that they are originally 

 of zoophytic or spongeous origin, and that the presence of the phos- 

 phate is attributable to deposition from the water of the Cretaceous 

 sea, as portions of ammonites and inocerami are found to contain 

 equally considerable quantities of phosphate. 



We now come to the Lower Greensand. — The "White or Bearsted 

 sand lies immediately under the Gault, upon the red ferruginous 

 sands. Tt is limited in extent, occurring only at certain places and 

 in difl'erent states of purity, White Heath, near HoUingbourne, af- 

 fording a very superior kind. I never heard of any fossils being 

 found in it. 



The next deposit is the ferruginous sand, with layers of ironstone. 



These beds rise rather abruptly 

 from beneath the Gault at Box- 

 iMIMl^ ley and Sandling, at an angle 

 or dip of 20 degrees. Sections 

 I of these beds may be seen at 

 the sides of most roads which 

 lead to the Gault, where the 

 of ferruginous sand has been cut through in 

 sandstone ; h b, etc., layers in a false strati- ^lany places. The most COm- 

 ncatiou. J? -1 • J.1 1. T 



mon lossiis m these beds nre 



casts of zoophytes or sponges, generally of a cylindrical shape. Some 

 appear allied to Siphonia, having a bulbous head, the sand being loose 

 or non-segregated in the interior. A few marine shells may be de- 

 tected by close inspection, chiefly Terebratulge. Trigonia alceformis 

 occurs in a bank of this sand near Thornhills. In Sandling Wood 

 about tw(Mii y Ivet of the sand is exposed, in which the ramification 

 of a mariiio plant is seen to great advantage. In places rings of 

 ironstone, circular and oblong, give an appearance of wavy lines, but 

 by a little examination it may be seen that these lines are sections 



