C R O 



C R U 



Werner. Colours white and grey ; occa- 

 sionally it is found with a reddish and 

 yellowish cast. It is composed of 47 parts 

 silica, 21 baryta, 15 alumina, 0'88 potash, 

 0-10 lime, 15 water. It occurs in small 

 quadrangular prisms terminated by four 

 rhombic planes, crossing each other. The 

 surface of the smaller lateral planes is 

 double plumosely streaked. It is found 

 in galena veins and agate balls in the 

 mines of Strontian, in Argyleshire, and 

 in other parts of Scotland ; also at An- 

 dreasburg, in the Hartz, and in Norway. 



CROY'LSTONE. Crystallized cauk. In this 

 the crystals are small. 



CRU'CIAL. (from crux, Lat. crucial, Fr.) 

 Transverse ; intersecting one another ; in 

 form of a cross. 



CRUCIFEROUS, (from crux andfero, Lat.) 

 The name given to a large order of plants, 

 whose petals, four in number, are so 

 arranged as to resemble a cross. The 

 radish, cabbage, stock, &c., are crucife- 

 rous plants. 



CRU'CIFORM. (from crux and forma, Lat.) 

 Cross-shaped ; in the form of a cross. In 

 botany, polypetalous flowers are so called, 

 when the petals are placed in the form of 

 a cross ; this is particularly the case in a 

 very large order of plants, which have 

 four petals, so arranged as to resemble a 

 cross. 



CRU'CIBLE. (crucibulum, Lat.) A vessel, 

 or melting-pot, made of earth, so named, 

 according to some, from its having been 

 formerly made in the shape of a cross ; 

 but, according to others, from the metals 

 being tortured in it by fire to compel them 

 to become gold. 



CRU'RA. (The plural of crus, Lat.) Ap- 

 plied to parts from their resemblance to 

 legs ; the legs. 



CRU'RAL. (crural, Fr. cruralis, Lat.) Be- 

 longing to the leg. 



CRUST, (kruste, Germ, crusta, Lat. croute, 

 Fr. crosta, It.) Any shell, hard coat, or 

 external covering. That portion of our 

 globe which is accessible to our inspection 

 and observation is called by geologists, 

 the earth's crust. It is this crust which 

 offers proper occupation to the geologist. 

 The greatest depth to which he has been 

 hitherto able to extend his observations, 

 from the uppermost strata to the lowest 

 beds, is from eight to ten miles ; a thick- 

 ness which, compared with the bulk of 

 the earth, does not exceed that of the 

 thickness of the paper which covers a 

 globe a foot in diameter. The inequalities 

 and crevices in the varnish applied over 

 the surface of such a globe would fairly 

 represent, and be in proportion to, the 

 highest mountains and deepest valleys of 

 the world. The mean density of the 

 earth's mineral crust has generally been 



taken at 2 '5 : according to De la Beche 

 2'6 would be a nearer approxima- 

 tion. 



CRUSTA'CEA. ) (from crusta, Lat.) The 

 CRUSTA'CEANS. $ Crustacea possess a hard 

 external covering, and numerous articu- 

 lated limbs ; antennae, and palpi. A 

 heart, with circulating vessels and gills, 

 and a nervous system. The crab, lobster, 

 sea-urchin, shrimp, &c., are examples. 

 Crustaceous animals possess the most 

 solid form of the skeleton met with in the 

 articulated classes. It is found in the 

 larger decopods to contain nearly half its 

 weight of carbonate of lime, and there is 

 also a considerable proportion of phos- 

 phate of lime, with traces of magnesia, 

 iron, and soda. These substances are 

 exuded from the surface of the true skin, 

 along with a tough coagulable animal 

 gluten, which connects all their particles, 

 and forms a thin varnish on the surface. 

 The colouring matter is generally beneath 

 this varnish, and on the exterior surface 

 of the calcareous deposit, but sometimes 

 it pervades the whole substance of the 

 shell. The history of fossil crustaceans 

 has been hitherto almost untouched by 

 palaeontologists, and their relations to the 

 existing genera of this great class of the 

 animal kingdom are but little known. 

 Some idea may be formed of their extent 

 in certain formations, from the fact, that 

 in the cabinet of Count Munster, there 

 are nearly sixty species collected from a 

 single stratum of the Jurassic Limestone 

 of Solenhofen. Dr. Rob. Grant. Pro- 

 fessors Buckland andFyfe. 



The Crustacea respire by means of 

 branchiae ; these branchiae, sometimes si- 

 tuated at the bottom of the feet, at others 

 on the inferior abdominal appendages, 

 either form pyramids composed of laminae 

 in piles, or bristled with setae ; and in 

 some cases consist seemingly wholly of 

 hairs. The Crustacea differ from the tes- 

 tacea in one most striking point of view : 

 lobsters, crabs, &c., cast their shell or 

 covering every year, whereas the testa- 

 ceous animals retain theirs as long as 

 they exist. The shells of crustaceous 

 animals appear to grow all at once, where- 

 as those of testaceous animals are evi- 

 dently formed by the animal adding gra- 

 dually to them, either annually or period- 

 ically, and they are all composed of 

 layers. 



CRUSTA'CEAN. } (crustacee, Fr. crust aceo, 

 CRUSTA'CEOUS. $ It.) Shelly, with joints. 

 The crustaceous animals possess a hard 

 shelly covering divided into parts by joints, 

 while the testaceous have a continued un- 

 interrupted shell. The crustaceous ani- 

 mals are the spiders of the sea. 

 CRUSTA'CEOUSNESS. The quality of having 



