325 
base line on which the sections of the railway were originally 
made, is Trinity high-water mark, the commencement of the 
railway may possibly be 70 feet above such datum. If the 
railway rises 30 feet in a mile, a line drawn from TO on the 
left side to 74.5 on the right will represent at once the true 
inclination of the railway, and the height of each portion of 
it above Trinity high-water mark. On the next sheet, sup- 
posing the section continued, the line will begin at 74.5 on 
the left and rise to 79 on the right. If now an interval of 
ten miles occurs, in vrhich there is no valuable geological 
information afforded, and in vrhich the rate of ascent is 
uniformly 30 feet in a mile — if a drawing is to be made of a 
cutting at the end of the ten miles, the line of railway will 
begin at 79 ft. + 300 ft. = 379 ft. on the left hand, and 
rising to 383.5 ft. on the rio^ht. In this manner, at whatever 
part of the railway a cutting occurs, it may at once be placed 
in its true relation to the base or datum line. When the 
general section of the cutting is thus drawn along the chart, 
there will always remain a considerable portion of the sheet 
unoccupied — the deepest cuttings will rarely occupy more 
than two inches in height, and whether this is near the top, 
or middle, or bottom of the sheet, (according as it is more 
or less elevated above the datum line,) matters not, as there 
will in any case be space left for two purposes, viz., to de- 
lineate any remarkable developement of thin strata or other 
peculiarity of structure on an enlarged scale of four feet to 
an inch, and thus all inconvenience arising from the minute- 
ness of the general scale is entirely avoided ; and on a still 
larger scale of delineation, to represent any fossils that are 
found within the limits of the section. The latter may either 
be the true size of the fossil, or magnified or diminished 
according as the dimensions may render expedient. 
A volume of accurate sections, with enlarged details of 
strata and accurate drawings of fossils, would be a valuable 
