Vertical section (from North to South) shewing Junction of Entrance Passage, and First Ascending Passage, looking West.

But if the distance on floor at which the axial line of the portcullis block, or, which is the same thing, of the first ascending passage, if produced, will strike,-be demanded, the distance will be very much less; viz. :

And distance at which said axial line strikes axis of entrance passage, measured transversely on floor, And distance at which roof of entrance passage is similarly struck,

= 958-0

= 975.5

= 993:3

These quantities were obtained for the means, by small special calculations of the following measures; but where the roughness of many of the broken surfaces prevented accuracy, and where a constant difference was found between the measures east and measures west.-(See Plate IV.)

The letters refer to the diagram following.