CONTENTS.
2
Methods for surface support—Continued.	Page
Artificial support.............................................^ _	54
Mushing.............................................................. 5!
Cogs................................................................. 52
Gob piers............................................................ 52
Gob stowage in rooms................................................  52
Concrete and masonry piers........................................... 53
Iron props..........................................................  53
Tests of roof-supporting devices.......................................... 54
Compressive strength of anthracite....................................... 54
Tests at Lehigh University............................................... 54
Dry filling................................................................... 56
Improved methods of gob stowage.......................................... 56
Blasting roof and floor in thinner beds.................................. 57
Gob piers and timber cogs................................................ 57
Concrete piers.........................................................   53
Dry filling with broken stone or sand.................................... 58
Suggestions for improvement in mining methods and pillar support.............. 60
Flushing................................................................. 60
Culm from old and from fresh-mined banks............................  61
Surplus mine rock.................................................... 61
River sand........................................................... 62
City refuse.......................................................... 62
Sand from distant points............................................. 63
Plans, specifications, and costs.............................................. 63
General conclusions........................................................... 69
Notes on sand for mine flushing in the Scranton region, by N. H. Darton...	72
Introductory statement................................................... 72
Rock for crushing........................................................ 72
Glacial till............................................................. 73
Alluvium................................................................. 75
River sand............................................................... 75
Appendix...................................................................... 77
Compressive strength of anthracite coal....................................... 77
Northern coal field...................................................... 79
Eastern Middle field..................................................... 82
Compressive strength of materials for roof support............................ 83
Tests at Lehigh University............................................... 83