An account is given of an investigation into the relationship between charge of explosive fired and seismic amplitude in routine quarry blasting. By keeping the instrument fixed over the investigation and by choosing a suitable recording position the effects of site factor can be considered to have been reduced to a practical minimum. The observations, which were made at distances of approximately 400 feet, give a relation between first peak amplitude and charge of the type, [Formula: see text] where the factor Q varied between 1 and 3 approximately and would apparently be assignable to varying blasting conditions. The results have also been reviewed in the light of an amplitude square relation modified on the supposition that the energy loss involved in practical blasting is a function of the charge.

The results of field and laboratory methods of density determination on a series of Coal Measure, Permian and Triassic rooks are presented and the different methods compared. It is concluded that the most satisfactory method is that of measuring the vertical change of gravity in a mine shaft. Nettleton's method is unsatisfactory to us, due to weathering of the rocks (particularly Magnesian Limestone) and possible effects from drift. Laboratory measurements are of variable value depending on the lithology and source of the samples.A method adopted to solve the problem of finding the true densities for use in a local gravity survey in N.E. England is given.

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Mr. Blundell's account of earlier work by A. F. Hallimond and J. T. Whetton (Bull. Geol. Surv. No. 2., pp 1–17, 1939) is inaccurate in certain particulars and is liable to mislead.

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