IF the mysterious sounds referred to by Prof. G. H. Darwin should turn out to be of subterranean origin, as is not unlikely the case, it may be that they are the reports arising from the process of “faulting” going on a small scale at a great depth, and not of sufficient intensity to produce a perceptible vibration at the earth's surface. In this connection I may recall an observation which bears upon the subject. When collecting materials for the report on the East Anglian earthquake of 1884, I was given a most circumstantial description of a loud report which was heard by the chief officer of the coastguard station at West Mersea during his watch between 1.10 and 1.20 a.m. on February 18 of that year. The sky was cloudless at the time, there was no flash such as might have been expected if the sound had been due to thunder or the explosion of a meteorite, and there was no artillery sufficiently within hearing to account for the sound. This report heard by the coastguard officer was afterwards found to have been felt as a slight shock at a house which was very much damaged by the earthquake which occurred a few weeks later (April 22), and we came to the conclusion that the officer and the inhabitant of the house in question had independently recorded a premonitory shock (“Report,” p. 40, by the writer, and W. White, “Essex Field Club Special Memoirs,” vol. i.). When Prof. Darwin's request for information shall have led to further knowledge as to the localities where the phenomenon has been observed, it would be of great interest to have in such places instruments for recording earth tremors.