Transcriber's Notes
Illustrations in this booklet are not always labelled in order of appearance, so full page diagrams may appear out of order. Fig. 4. seems to have been ommitted and is not found (or referenced) in any of the online sources. Minor corrections made to punctuation. inconsistent hyphenation and spelling.
In particular:
- p7. "rceiving" changed to "receiving".
- p11. "wabble" has been left - it appears to be a variant spelling of wobble.
- p18. "overhanging ledges or these materials" changed to "overhanging ledges of these materials".
- p22. "only few men" changed to "only a few men"
- TABLE II.
"Loose gravel 1 30 1 30 2 60 3 90 4 12"
changed to
"Loose gravel 1 30 1 30 2 60 3 90 4 120" - p50. "steam or air driver" change to "steam or air driven"