geological sections. The distortion of scale completely pre- 
vents the very intention of the section, which is to convey a 
correct idea of the relative thickness and inclination of strata. 
In surface models, where the intention is to afford a general 
idea of a district, it is sometimes desirable to enlarge the ver- 
tical scale, and this was done in the model of Dean Forest, 
which, on a former occasion, I had the honor of submitting to 
this Association. Since that time I have constructed a model 
of the principal coal field of that district on the natural scale : 
the result is, that though the latter is unquestionably the 
correct and most scientific mode of construction, yet it gives 
a fallacious idea of the nature of the surface — the steep hills 
and narrow valleys of that romantic forest sink into gradual 
undulations, which would never be recognised as the type of 
a picturesque country ; and the two models, which are now 
placed in juxta-position, in the Museum of Economic 
Geology, aff'ord a good practical lesson as regards the 
proportionate scales to be employed. To give to the 
mind a graphic idea of a country, the vertical scale should 
be increased about three times; but when the object is to 
convey to the mind clear ideas of the geometrical relations 
of the surface as they are in nature, and not as they are 
presented on the retina, then a uniformity of vertical and 
horizontal scale is to be observed. In geological sections, 
however, nothing but necessity can justify the distortion of 
scale, and the Committee, fully aware of the great scientific 
value of correct proportion, decided that the charts should 
be constructed accordingly, so that the drawings thereon 
should be a faithful transcript of nature. 
Another advantage proposed to be gained by the form of 
chart engraved by the Committee is, that, ranging as it does 
600 feet in height, it admits of each part of the railway being 
shown at its proper elevation above the datum line of the 
railway, and also the rate of ascent. Thus, if the datum or 
