Rochet as worn by 

 Anglican bishops 



whilst his escapades were the 

 talk of the town. He patronised 

 and helped many men of letters. 

 Worn out with debauchery, he died 

 July 26, 1680. Many of his writings 

 were too obscene lor publication, 

 but Tonson published an edition in 

 1741, and an expurgated edition 

 appeared in Johnson's collection. 



Rochet (French ; Ital. roccello). - 

 Ecclesiastical vestment. A kind 

 of surplice, of fine linen, it is 

 now worn by 

 bishops under, 

 instead of over, 

 the c h i m e r e 

 (q.v.). The 

 name dates 

 from about the 

 17th century, 

 but the gar- 

 ment is much 

 older. In its 

 medieval form 

 it had narrow 

 sleeves, which 

 grew to re- 

 markable size, 

 in English 

 usage, in the 

 17th century. 

 Rock. Geological term for 

 certain hard masses of the earth's 

 crust. A rock may be an aggre- 

 gate of mineral particles of one 

 kind only; but most rocks contain 

 several minerals, and their chemical 

 composition varies. The rocks form- 

 ing the great mass of the earth re- 

 main unknown, and are probably 

 far poorer in silica and far richer in 

 heavy metals, such as iron, than 

 those of the crust. Parts of the 

 crust, or of layers not far below it, 

 are either molten or subject at 

 various times to melting, and 

 their materials sometimes reach 

 the surface in the form of lava. By 

 analogy with these highly heated 

 and fluid masses, the constituents 

 of which crystallise when cooling is 

 sufficiently prolonged, we conclude 

 that a number of rocks now formed 

 of crystalline minerals were at one 

 time molten in the crust. These 

 rocks cut across the structures of 

 other masses, send out veins into 

 adjacent fissures, and sometimes 

 include fragments of the rocks into 

 which they have intruded. 



Such rocks are grouped with 

 superficial lavas under the name 

 igneous, which implies, not fiery 

 combustion, but consolidation 

 from a molten state. Slow cooling 

 promotes in them coarseness of 

 grain ; rapid cooling allows some 

 of the constituents to remain un-^ ' 

 crystallised, i.e. in a glassy state. 

 We conclude that the basalts of 

 Vesuvius and the diorites and 

 granites that form mountainous 

 scenery in the British islands are 

 alike igneous rocks. 



6656 



Another great group of rocks 

 is styled sedimentary. Wherever 

 rock of any kind is exposed at 

 the earth's surface, it comes under 

 the action of forces which cause it 

 to break down and crumble. The 

 mineral particles, moreover, de- 

 compose in various degrees, accord- 

 ing to their chemical composition. 

 Quartz is practically indestructible, 

 and its fragments go to form sands, 

 becoming smaller and ultimately 

 rounded as they travel, until they 

 come to rest in a valley-floor or sea, 

 and are held together to form sand- 

 stone by the deposition of some 

 mineral cement. Felspars break up 

 chemically as well as mechanically, 

 and their aluminium silicate takes 

 up water and forms new sub- 

 stances which are the bases of 

 clays. These clay particles become 

 sifted out by running water from 

 associated coarser matter, are at 

 length deposited in quiet places, 

 and are compacted into the sedi- 

 mentary rocks, the clays and shales. 



Many constituents of decaying 

 rocks pass into solution in natural 

 waters, and for the most part find 

 their way into the sea. New 

 combinations may arise from these 

 through the activity of organisms, 

 leading notably to the deposition 

 of calcium carbonate as calcite or 



Rockbieakei. 



Diagrams explaining 

 machines. See text 



aragonite. The shells and other 

 hard parts of such organisms go 

 to form the important sedimentary 

 rocks known as limestones. 



Lastly, igneous or sedimentary 

 rocks in which new structures, or 

 new minerals, or both, have arisen 

 through the action of pressure or 

 heat, or commonly of both, in the 

 earth's crust are styled meta- 

 morphic. Slate, with its planes of 

 parting, usually quite independent 

 of the sedimentary layer-structure ; 

 schist, with minerals developed 

 along certain planes, which may be 

 those of original bedding or may 

 be superinduced by crush and 

 flow under earth -pressure ; and 

 gneiss, which may be a coarser 

 type of schist, or may represent 

 an intimate mingling of igneous 

 and sedimentary matter, are repre- 

 sentative types of metamorphic 

 rocks. See Geology ; Petrology ; 

 consult also Text Book of Pe- 



ROCK BUTTER 



trology, F. H. Hatch and R. H. 

 Rastall, 1913-14; Igneous Rocks 

 and Their Origin, R. A. Daly, 1914. 



Orenville A. J. Cole 



Rockall. Islet of the Atlantic 

 Ocean. A small rocky peak, about 

 100 yards in circumference, it 

 stands about 230 m. W. of N. Uist, 

 Hebrides. It is believed to be 

 the only existing fragment of the 

 lost or Palearctic continent. 



Rockbreaker OR STONEBREAKER. 

 Machine for breaking rock or 

 stone. There are four classes 

 of rock or stone breaking ma- 

 chines : stamps, jaw breakers, 

 disintegrators, and rolls. The 

 most important is the Blake jaw 

 breaker type. 



It consists of two large flat jaws, 

 A, B (Fig. 1), of hard iron or steel, 

 each serrated on one face forming 

 huge teeth. One is fixed vertically 

 to a massive frame of. iron, which 

 carries all the working parts ; the 

 other is hung from a horizontal 

 axle, so that it may swing freely. 

 The serrated surfaces of the jaws 

 face each other at an angle form- 

 ing a large mouth, wide at the top, 

 narrowing as it goes down. By 

 means of a toggle C and links the 

 hanging jaw is oscillated at its 

 lower end towards and from the 

 fixed jaw. D is the toggle lever, 

 E a wedge adjust- 

 ment. The large 

 stone is thrown 

 into the top of the 

 mouth and is 

 broken between 

 the two jaws, the 

 pieces getting 

 smaller as they 

 descend to the 

 bottom of the 

 mouth, out of 

 which they finally 

 drop. Machines 

 on this principle are almost univer- 

 sally used wherever stone is to be 

 crushed on any important scale. 



Another form of jaw breaker, 

 shown in Fig. 2, is known as the 

 gyratory breaker. In principle the 

 action is the same as in the Blake 

 machine. A is a gyrating spindle 

 with cone jaw, B, B fixed jaws. 



An important form of rock- 

 breaker has been introduced for 

 breaking rock under water. It 

 consists of a massive bar with its 

 lower end of pointed steel, which 

 is dropped repeatedly through the 

 water from a crane upon the point 

 where it is desired to break up the 

 rock. The crane and operating 

 gear are mounted on a barge, 

 Thich can be moved as required. 



Rock Butter. In mineralogy, 

 name given to a variety of halo- 

 trichite or of chrismalite. Yellow 

 in colour, it is found at Hurlet 

 and Campsie in Scotland. 



working of the 



