C L I 



[93] 



C L U 



CLEA'VAGE. A peculiar fracture, im- 

 pressed by nature, which is some- 

 times mistaken for stratification. 

 This is prettily described by Dr. 

 Mantell : " If I take a flint and 

 break it at random, it still preserves 

 a conchoidal fracture, a sharp 

 cutting edge ; and sub-divide it as 

 I may, it still retains the same 

 character. If I shiver to pieces 

 calcareous spar, every fragment 

 presents, more or less distinctly, a 

 rhomboidal form ; so true is the 

 remark, that we cannot break a 

 stone but in one of nature's join- 

 ings." 



The regular partings or cleavages 

 in many slate rocks which inter- 

 sect the beds, nearly at right 

 angles to their dip or inclination, 

 have often been mistaken for strata 

 seams, and have led geologists of 

 some eminence to draw very er- 

 roneous conclusions. 



"Cleavage means the superin- 

 duced fissile structure of clay- 

 slate ; cleavage pays no regard to 

 the laminae of deposition, or original 

 bedding of the rock, but frequent- 

 ly cuts right across it." Jukes. 



"Where only part of a bed is 

 exposed, it is often difficult to 

 distinguish the lines of cleavage 

 from the true planes of stratification; 

 but the doubt may be cleared by 

 observing the upper and under 

 surface of the bed at the line of its 

 junction with its superstratum and 

 substratum, especially if these be 

 of a different substance. Conyleare 

 and Phillips. 



CLEAE'VLANDITE. A mineral, to which 

 this name has been given after 

 Professor Cleaveland ; it has been 

 also called albite. 



CLIMATIFS BETICULATTJS. An ichthy- 

 olite of the old red sandstone, de- 

 scribed by Agassiz in his Poissons 



CLI'NKSTONE. (So named from its 

 yielding a metallic sound when 

 struck.) Called also phonolite, a 

 felspathic rock of the trap family. 



In basalt or wacke*, when the 

 felspar greatly prevails, and the 

 texture becomes nearly compact, 

 basalt passes into clinkstone ; again, 

 when clinkstone has a more earthy 

 texture, it passes into claystone. 

 Clinkstone often contains imbedded 

 crystals of felspar, and then be- 

 comes a trap-porphyry, varying in 

 colour according to the prevailing 

 ingredients of its base. The colour 

 of clinkstone is grey, of various 

 shades. According to Gmelin, 

 natron and potash characterize 

 clinkstone; iron and magnesia, 

 basalt. 



CLINO'METER. (from K\IVW and juterpov, 

 Gr.) An instrument, invented by 

 R. Griffith, Esq., for measuring 

 the dip of mineral strata. The 

 following description of the clino- 

 meter is extracted from a paper by 

 Lord Webb Seymour, presented to 

 the Geological Society. The clino- 

 meter consists of two parts, the 

 plate and the quadrant. The plate 

 is circular and of brass ; it is sup- 

 ported by three feet placed at 

 equal distances, and made of wood, 

 with their ends flat and broad. 

 The clinometer may be used to 

 determine the position of any plane 

 surface to which the plate may be 

 applied so as to admit of obser- 

 vation with the quadrant. 



CLO'VATE. In conchology, thicker 

 towards the top, elongated towards 

 the base. 



CLO'VEN. In botany, leaves are called 

 cloven, when the margins of the 

 segments and fissures are straight. 



CLTJNCH. A provincial term for a 

 sort of indurated clay which is 

 found dividing the coal seams. 

 The clunch yields those infusible 

 kinds of clay which are adapted for 

 fire-bricks ; it varies in hardness, 

 and is black, grey, yellow, white, 

 &c. In the coal series it is gene- 

 rally found immediately beneath 

 each bed of coal, and where it 

 crops out at the surface becomes 

 soft clay. 



