112 Proceedings of the Association 
When the measurements are taken, not on a level, but over an 
inclined or undulating surface, the operation of levelling, deter- 
mines the position of the line connecting the extremities of the 
section, with reference to a horizontal line in the same vertical 
plane, reaching from the higher to the lower bed of the series. 
The length of Abia horizontal line also becomes known, since the 
dip of the beds is supposed to be ascertained, and the quantity d 
thus computed, enters the formula as before. It is evident that 
this determination of the horizontal distance here admits of two 
ases, according as the underlying or the overlying bed is topo- 
graphically the more elevated at the outcrop. In the former case 
the horizontal is shorter, and in the latter longer, than the inclin- 
ed line of measurement. 
Prof. J. mentioned that the section which he exhibited had 
been constructed in the manner above explained, and that speci- 
mens of rock, coal, slate, &c., collected from point to point along 
a tunnel driven obliquely to the place of dip had been used to 
furnish the coloring ee appropriate to the respective - 
of the section 
- Having marked out the limits of each bed, a moderately thick 
e of gum tragacanth and gum arabic in equal. pen is spread 
over one of the spaces required to be colored, and is not allowed 
to extend to the next. The pulverized rocky sintétiel is then 
sifted over the surface till the paste is completely covered. The 
excess is then thrown from the sheet, and the adjoining spaces are 
successively coated in a similar way with their appropriate pow- 
ders. 'T’o exhibit coarser and finer materials in the same rock, a 
coarser sieve is first used to sprinkle sparsely a quantity of gran- 
ules over the paste; the finer powder is then applied to occupy 
es ee spaces. Conglomerates belonging to the forma- 
nted, were thus exhibited on the section. When all 
te tens have been applied and time allowed for drying, a coat 
of pure map-varnish is applied to prevent injury to the surface 
from rolling or transportation. ‘This precaution is perce 
when the section is to be permanently suspended. 
Prof. Johnson also called attention to some facts in the ria tened 
condition and artificial production of gypsum. Adverting to some 
remarks during the present session on the calcareous deposits in 
steam boilers, ‘he exhibited specimens of scale from a sea steam- 
er’s boiler accumulated during a run of sixteen hours over the 
na banks. It is erystallized in prismatic fibres crossing 
thickness, and has a sp. gr. of 2°69, Analysis proved this scale 
poe a dihydrated ‘eeu — of 
~~ Lime 39-67 - 2 pone 
> sulphuric wey - 5425 = 2. 
~ Water, 6: 
4 O7 1 ohh ¢ & _ 
bore consequently aingisliod im composition ‘ariel 
