ON COLOURING GEOGNOSTICAL MAPS. Stgjj 



Werner remarks, that formation-suites may aiso 

 be represented in colours f : thus, the slate- forma- 



used by Werner, to express sand, inflammable substances, 

 chalk, salt, iron, and copper, have been long known ; but 

 the others are of his own framing. Thus, the curved line 

 in the symbol of serpentine, &c. intimates, that the rock 

 is of a magnesian or greasy nature ; the square symbol 

 intimates, that the rocks to which it refers, generally 

 break into a quadratic shape, as quartz ; the lengthened 

 square, that the rock breaks into tables, as gneiss ; the 

 rhomboidal-shape, that the rock breaks into sharp -angled 

 pieces, as porphyry ; diagonal-streaks in a square, when 

 drawn from right to left, or across from one side to the 

 other, intimate, that the rock has a slaty texture, as gneiss 

 and topaz-rock \ perpendicular streaks, or lines in a square, 

 intimate, that the rock wants the slaty structure, as 

 granite ; a diagonal line from the left to the right, always 

 marks rocks of the trap-formation, as greenstone \ a small 

 oval in a square, expresses the occurrence of masses of after- 

 formation in a rock, and is used as the symbol for amyg- 

 daloid ; small black squares inclosed in a larger "square, 

 express embedded crystals, as in porphyry shorter and 

 shorter lines above each other, are the symbol for clay j 

 and when conjoined with dotts, express clay and sand to- 

 gether. All these signs are more or less combined to- 

 gether, so as to form the different symbols. Thus, the 

 symbol of greenstone- slate is a lengthened square, in- 

 cluding two lines drawn from the right hand to the left, 

 and one from the left to the right : The lengthened square, 

 intimates, that it has a slaty fracture ; the two lines 

 from the right hand to the left, that it has two constitu- 

 ent parts \ and the line from the left to the right, that it 

 belongs to the trap-formation. 



f For explanation of formation-suit es^ see Elements 

 " of Geognosy," p. 88., &c, 



