D)-. T. Stacey Wilson — The Making of Geological Models. 261 



shaping are gouges and chisels, and for the smaller work a sharp 

 penknife, the material having the consistency of rather hard cheese- 

 On account of the ease with which the waxed felt can be cut 

 the surface of a model can be carved into a much better representation 

 of the relief of a country than is the case with wood or other 

 materials, and outcrops can be rendered in a much less conventional 

 manner than hitherto. 



Faulting can be shown by cutting the model clean through along 

 any given line and joining the severed edges together after heating 

 them slightly ; they reunite with the utmost ease into a solid block, 

 which can be carved into shape as before. 



Folding may be produced in two ways. Either the complete 

 thickness of several layers may be kept warm and bent as a whole 

 into the desired shape ; or else, and this is always necessary when 

 complicated folding has to be rendered, a basal model of the fold 

 types may be carved in wood or cast in plaster, and the waxed felt 

 laid on it and fitted in layer by layer. The surface is, of course, 

 worked up afterwards with the knife or gouge. 



Obviously the faults of folds and faults, unconformity, and 

 thrusting can be readily dealt with on the same lines. 



A modification of the method must be employed in cases where 

 jt is important to deal with beds of varying thickness or those which 

 thin out altogether. This method is also of great use in treating 

 a complicated country such as that to be immediately referred to. 

 For this purpose wool-clippings from a carpet factory, or ordinary 

 felt scraps cut up and teased out, are folded in muslin, soaked in 

 melted paraffin, squeezed out, and then spread out into a layer of 

 the requisite thickness, pins having been previously driven into the 

 base on which one is working, of a height corresponding to the 

 thickness of the stratum. Sculpture is carried out as before. 



In order to show the application of this process to the modelling 

 of a particular district it will be most convenient to describe the 

 actual making of a model which I made in 1901 to illustrate 

 a paper on the Harlech district by Professor Lapworth and myself, 

 read before the Geological Section of the Birmingham Natural 

 History and Philosophical Society, March 28th, 1900. 



1. The lowest bed on the series dealt with was taken as the 

 floor of the district, and the depth of its base below a convenient 

 plane or base-level (parallel to the sea-level) was calculated at 

 a sufficient number of points in the map to permit of the drawing 

 of contour-lines on the bed so as to give the general character of 

 the folding and faulting. 



2. A vertical scale was chosen and contour-lines showing a depth 

 of 4) i-j 4 inch, etc., below base-level were drawn on the surface of 

 a block of wood. 



3. This surface being taken as the base-level, holes were bored with 

 a bradawl along the contour-lines to depths of j, |-, f inch and so on. 



4. With a gouge and chisel the surface of the block was now cut 

 down to the bottom of the holes, as is done by a sculptor in roughing 

 out his marble. 



