Notice of a Geological Model. 81 



mits of shewing the objects solidly, in relief; and according to 

 their actual proportions, whenever practicable. I mean the pro- 

 cess of modelling areas of country, in preference to any other 

 method of representation ; whether by drafts, diagrams, tables, 

 maps, sections or other customary means. Under this impression, 

 and with a view to convey these sentiments in a useful direction, 

 I have made some exertion to complete, for this occasion, a spe- 

 cimen of the art, illustrative of several hundred square miles of 

 interesting country in the interior of this state ; but have only 

 during the intervals of the present meeting of geologists, found 

 time to prepare and commit to paper the following observations. 



With the best assistance which art can confer, by means of 

 horizontal or vertical or concentric shading, or by the most elabo- 

 rate arrangement of lines upon a plane surface, to produce the 

 effects of light, shadow, height, depth and perspective, such pro- 

 cesses, it is universally conceded, fail to accomplish what is sim- 

 ply effected by modelling. If to these desiderata in geological 

 illustrations, and to those other lines which are indispensable to 

 topographical or local delineation, we add those which are inten- 

 ded to represent the courses and the inclination of strata, and the 

 breadths and separate characters of formations, the difficulties 

 attendant on lucid illustration are heightened, in any process short 

 of modelling. 



Whenever the scale, upon which a given area is protracted, is 

 sufficiently large to permit an approximate correspondence be- 

 tween the horizontal and the vertical admeasurements, the effect 

 is perfect. The utility of the work is enhanced, in as much as 

 it combines the exhibition of both transverse and horizontal sec- 

 tions on the field of survey ; and illustrates not only the external 

 features and physical geography of the district, but enables the 

 interior structure, the grouping of its mountain masses, the incli- 

 nations, bearing, direction, contortions and dislocations of the 

 strata into which those formations and masses are subdivided, to 

 be exhibited in a simple yet very striking and appropriate manner. 

 With the addition of superficial coloring, the pictorial character 

 of the region represented, can be as accurately depicted as in a 

 highly finished landscape. Perhaps even more so ; in as much 

 as the positions of all surrounding objects, and of all accessory de- 

 tails, are defined with geognostic accuracy in the one case, rather 

 than imperfectly traced in the other, however experienced may 



Vol. xLi, No. 1.— April-June, 1841. 11 



