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A marine deposit of silicious sands 

 and sandstone of various shades of 

 green, red, brown, yellow, ferugi- 

 nous, grey, and white, with subor- 

 dinate beds of cherts and silicious 

 limestones, constitute the formation 

 called the Shanklin sand, or the 

 lower green sand. It is the lowest 

 member of the . cretaceous group, 

 intervening between the gault 

 above and the weald clay below. 

 The beds consists of an aggregation 

 of sand, with comminuted shells 

 and fragments of corals, impreg- 

 nated with iron, and containing the 

 remains of myriads of shells, poly- 

 paria, &c. Dr. Fitton divided the 

 Shanklin sand into three distinct 

 parts : the first or uppermost con- 

 sisting of sand, with irregular con- 

 cretions of limestone and chert, 

 sometimes disposed in courses 

 oblique to the general direction of 

 the strata. 



The second consists chiefly of 

 sand, but in some places is so mixed 

 with clay, or with oxide of iron, as 

 to retain water: it is remarkable 

 for the great variation in its colour 

 and consistency. 



The third and lowest group 

 abounds much more in stone ; the 

 concretional beds being closer 

 together and more nearly continu- 

 ous. The Shanklin, or lower green, 

 sand, is separated from the upper 

 by the gait or Folkstone marl. 

 SHARK, (from icap^apla^, Gr.) The 

 squalus of Linnaeus. A genus of 

 fishes belonging to the family 

 Selachii, order CJiondropterygii 

 Branchiis Fixis. The shark is a phos- 

 phoric fish. That tribe of sharks, 

 called by the French Eeguins, 

 which is thought to be synonymous 

 with the carcharias of the Greeks, 

 and one of which was probably the 

 monster that swallowed Jonah, are 

 stated to exceed thirty feet in 

 length. The genus of sharks may 

 be considered as one of the most 

 universally diffused, and most vora- 



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cious, of modern fishes. Several 

 rows of teeth are lodged in each 

 jaw, but one only of these rows 

 projects, and is in use at the same 

 time ; the rest lying flat, but ready 

 to rise in order to replace thoee 

 that have been broken off, or worn 

 down. The shark is oviparous or 

 ovo-viviparous, according to cir- 

 cumstances. The vertebral column 

 is prolonged into the upper lobe of 

 the tail, and the tail is of great 

 service in enabling the shark to 

 turn its body so as to bring the 

 mouth, which is placed downwards 

 beneath the head, into contact with 

 its prey. Sharks appear to have 

 existed throughout every period of 

 geological history. M. Agassiz 

 has separated the sharks into three 

 sub-families, each containing forms 

 peculiar to certain geological epochs, 

 and which change simultaneously 

 with the other great changes in 

 fossil remains. The first of these 

 sub-families, or the Cestracionts, 

 commence with the transition 

 strata, appearing in every subse- 

 quent formation till the commence- 

 ment of the tertiary. Of the Ces- 

 tracionts, one representative only 

 now remains, namely, the Cestra- 

 cion Philippi, or Port Jackson 

 shark. The Cestracionts possessed 

 large polygonal, obtuse, enamelled 

 teeth, covering the interior of the 

 mouth with a kind of tesselated 

 pavement. The second sub-family, 

 or Hybodonts, commenced with 

 the muschel-kalk, is found through- 

 out the whole of the oolitic deposits, 

 and disappears at the commence- 

 ment of the cretaceous group. The 

 teeth of the Hybodonts were inter- 

 mediate between the blunt polygo- 

 nal teeth of the Cestracionts and 

 the sharp-edged cutting teeth of 

 the Squaloids. The third sub- 

 family, termed Squaloids, appeared 

 at the commencement of the chalk 

 deposits, and continues downwards 

 to the present period. In the 

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