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IX. On Colouring Geognostical Maps. 

 By Professor Jameson. 



(Read $th April 180.8.J 



In constructing geognostic maps, after having 

 delineated the aspect of the surface of the country 

 we have examined, our next business is to exhibit, 

 as far as possible, by means of colouring, a true 

 and harmonious representation of the alternation, 

 extent, and relative position, of the different rocks 

 that appear at its surface. Various methods have 

 been adopted for accomplishing this object. In 

 some maps the boundaries of the different rocks 

 are marked by a continuous or dotted line, and 

 the inclosed space representing the rock, by a 

 particular symbol ; in others the inclosed spaces 

 are distinguished by lines running in different 

 directions, or by dotts of various magnitudes ; 

 lastly, in others the inclosed spaces are coloured. 

 Of all these, this last is the preferable method, 

 and is besides that which has been most generally 



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