389 



Conformable. When strata are arrang«fl parallel to each other, like 

 the leaves of a bo^^k, they are saivl to bu confonii^ible. Other strata ly- 

 ing across the edge^ of thes«e may he coiifurraable among themselves, 

 but unconformuble to the first set of ptrata. 



Conylomerute, or Pndtlingstoiie. Rocks composed of rounded 

 masses, pebbles and gravel, cemeuted together by a silicious, calcareous, 

 or argillaceous cement. 



Cretaceous. Belonging to the chalk formation. 



Crop out, and out crop. Terms employed by geologists and mining 

 engineers, to express the emergence of rock, in place, on the surface of 

 the earth at the h)Cality where it is said to crop ouL 



Crystalline. An assembi ige of imperfectly defined crystals, like loaf 

 suffar and common white marble. 



Delta. Alluvial land formed at the mouths of rivers. 



DeniiJution. A term used to express the bare nUite of the rocks 

 over wiiich currents of water have formerlv swept, and laid the rocks 

 bare, or excavated them to form valleys o!" denudalion. 



Deoxidize. To separate oxygen from a body. 



Detritus. Broken and removed portions of rock which have been 

 operated upon by waters or the atmosphere; frequently transported by 

 currents to of reat distances. 



Dykes. A kind of vein intersecting the strata, and usually filled 

 with some unstratifi^d igneous rock, such asgtaiiite, trap or lava. These 

 materials are supposed to have been injected in a melted state into 

 great rents or fissures in the r cks. 



Diluiium and Dihivion. Deposits of boulders, pebbles and gravel, 

 which many geologists have supjiosed were j>roduced by a diluvial wave 

 or deluge, sweeping over the surface of tiio earth. 



Dip. \Vbere htrata are not horizontal, the direction in which their 

 planes sink or jilunge, is called the direction of the dip, and the angle 

 of inclination, the aHgle of dip. 



Dolomite. A magnesian limestone belonging to the primary class. 

 It is usually granular in its structure, and of a friable texture. 



Dunes. Sand raise I into hills and drilLs by ih« wind, 



Eartlis Crust. The sui>erficial parts of our planet which are ac- 

 cessible to human observation. 



