C H A 



[44] 



CHE 



north coast. The chalk formation is 

 composed of six divisions, namely, 1. The 

 Maestricht beds ; 2. The upper chalk 

 with flints ; 3. The lower chalk without 

 flints ; 4. The Upper green sand ; 5. The 

 gault; 6. The lower green sand. The 

 whole of these are marine deposits. It 

 must however be kept in mind that this 

 order is far from constant. The mem- 

 bers of the cretaceous group are ranked 

 as the last of the secondary period ; and, 

 in the order of superposition, are placed 

 above the wealden, and below the earliest 

 of the tertiary period, or eocene. The 

 greatest thickness of the chalk strata in 

 England may be estimated at from 600 

 to 1000 feet. The organic remains in 

 the chalk formation are exclusively ma- 

 rine. The nodules and veins of flint 

 which occur in the chalk, show ,#rat 

 water holding silex in solution must have 

 been very abundant at the cretaceous 

 period, although we are ignorant by what 

 means silex may be dissolved in water. 

 Mammalia are not known in the creta- 

 ceous rocks. 



The chalk hills of England are bounded 

 by a line which stretches from south-west 

 to north-east, and they form three prin- 

 cipal mountain ranges. The first, leaving 

 Berkshire, runs north through Bucks, 

 Bedfordshire, and Hertfordshire, to Gog- 

 magog hills, near Cambridge. The se- 

 cond, passing from Bei'kshire eastward, 

 stretches through Surrey, where it forms 

 the Hog's Back, a beautiful ridge extend- 

 ing from Farnham to Guildford, and 

 then appears at Boxhill. This branch 

 forms the hilly country and the Downs 

 north of Reigate, Bletchingly, and God- 

 stone. It enters Kent to the north of 

 Westerham, and extends to Folkstone 

 and Dover. One division of this ridge 

 is continued to the north coast of Kent, 

 and terminates at the North Foreland. 

 The third range, leaving Wilts and Berks, 

 enters Hants, and to the south passes 

 round Petersfield, then stretching to the 

 east, forms a barrier against the sea along 

 the coast from Chichester, constituting 

 the South Downs, ranging from Maple- 

 durham to Beach-head. 

 CHA'LICO-THERIUM. An extinct animal, 

 belonging to the order of Mammalia 

 allied to the tapir, and referrible to the 

 miocene period. 

 CHALY'BEATE. (from chalybeus, Lat. cha~ 

 liMe, Fr.) Impregnated with iron or 

 steel ; holding iron in solution, as cha- 

 lybeate springs. 



CHAM A. {animal a chiton.} A genus o 

 inequivalved adhering bivalves, with un- 

 equal incurvated beaks. It is placed both 

 by De Blainville and Lamarck in the fa- 

 mily Chamacea, together with Diceras 



Etheria, &c. Bruguiere limits this genus 

 to those shells possessing a single hinge- 

 tooth only. Many species have been 

 found fossil, more particularly in the 

 neighbourhood of Paris. The shells of 

 this genus are inhabitants of the ocean, 

 and live in deep water. Twenty-five 

 species have been described ; one only 

 of these has been discovered in our seas, 

 namely, the Chama Cor. 



HAMA'CEA. A family of bivalves, placed 

 by Lamarck in the order Dimyaria, and 

 by De Blainville in the order Lamelli- 

 branchiata. It comprises the genera 

 chama, diceras, etheria, isocardium, tri- 

 gonia, &c. 



CHA'MA GIGAS. A species of chama in- 

 habiting the Indian ocean ; it is the 

 largest and heaviest shell yet discovered, 

 being sometimes of the enormous weight 

 of 530 pounds, and its occupant so large 

 as to furnish one hundred and twenty 

 men with a meal ; it is said to be very 

 palateable. 



CHA'MBERED. (chambre, Fr.) Divided 

 into compartments by septa : The cham- 

 bered shells have also been called multi- 

 locular. The fossil chambered shells are 

 exceedingly numerous, and afford proofs 

 of not only having performed the office of 

 ordinary shells, as a defence for the body 

 of their inhabitants, but, also, of having 

 been hydraulic instruments of nice ope- 

 ration, and delicate adjustment, con- 

 structed to act in subordination to those 

 universal and unchanging laws, which 

 appear to have ever regulated the move- 

 ment of fluids. The history of chambered 

 shells illustrates also some of those phe- 

 nomena of fossil conchology, which re- 

 late to the limitation of species to parti- 

 cular geological formations ; and affords 

 striking proofs of the curious fact, that 

 many genera, and even whole families, 

 have been called into existence, and again 

 totally annihilated, at various and suc- 

 cessive periods, during the progress of the 

 construction of the crust of our globe. 

 Prof. EucUand. 



CHA'OS. (Lat. chaos, Fr.) A matter 

 without form ; the first matter of which 

 poets supposed all things to have been 

 made in the beginning. 



CHA'OTIC. Confused ; thrown together in 

 one vast heap, without any order or re- 

 gularity. 



CHEIRO'PTER. (from x 'i manus, and 

 Trrtpoi/, ala.) An animal having the fin- 

 gers elongated, for the expansion of 

 membranes which act as wings, as in the 

 Vespertib'o or bat. The Cheiroptera, 

 according to the arrangement of Cuvier, 

 form the first family of Carnaria. 



CHEIRO'PTEROUS. Furnished with elon- 

 gated fingers, or toes, for the expansion 



