These final reports are useful in planning work for future years, in estimating future costs, and by comparison with previous years, in determining on the basis of percentage the effectiveness of the work. A system of tags has been suggested to avoid duplication of numbers, misreading of numbers of other normal errors. Each tag would have three stubs, one stub to be retained when the tree was spotted, one when felled, and one when rolled. In conclusion a few facts will be given concerning the work actually done during the two years in which appropriations have been available. Their form is wholly or partly determined during flight through the air, while in a liquid state.
Bombs naturally fall into two classes.
Those which start as liquid masses, acquire some symetrical form during flight and retain this form upon landing. These forms are very characteristic, usually symmetrical and unless broken after falling, show fracture surface. A second class of these bombs starts as a solid angular fragment which has either been reheated in the volcano hearth until the surface has melted or has been dipped in molten lava in the course of its upward movement through the crater. Such a bomb may have any form, depending upon the shape of the original fragment, and the coating may have any thickness. The bombs of either of the classes may be breadcrusted.