the catchment basin controlling the volume of the rivers was large, and where permeable strata prevailed. Thus it was with London, and the extension of that city had worked along in those directions where water was got with the best facility. The second part of the address related to the work of the Royal Commission to examine into the coal fields and the coal supply, under which Dr. Prestwich was charged with the study of the districts covered by the later Secondary and the Tertiary strata, with the special object of inquiring "into the probability of finding coal under the Permian, new red sandstone, and other incumbent strata. The discussion of this subject implied a survey of the coal fields of England, France, and Belgium, and the possible connection through strata underlying the formations named. Several regions were indicated where trials for coal might be made, which it was admitted, however, might be attended with considerable uncertainty. But whether successful or not as to coal, such trials near London could hardly fail of some important results; for it was "possible that the lower greensands would at some spots be reached, so that the inestimable additional benefit of a large and steady supply of pure water might also be obtained, and with proper care to prevent interference might be maintained for all time."
Commending Dr. Prestwich's investigation of the sources of the water supply of London, and the presentation of the results in his book on that subject—"a masterpiece of minute observation and close and accurate reasoning"—Prof. J. W. Judd observed that the geologist could point to the work "with pardonable pride as affording convincing proof that his science has now acquired a character for exactness analogous to that which is justly regarded as the crowning attribute of astronomy." His predictions as to the finding of coal underneath the Secondary rocks across the kingdom were likewise justified in the results of borings made near Dover.
An important practical application of Dr. Prestwich's investigations of the geology of the English Channel, not anticipated when they were begun, was illustrated in his report on the subject to the Institution of Civil Engineers, presented in December, 1874. This report was described by Nature as being a most excellent example of the indispensability of thorough scientific research as a basis for the useful arts, and of the way in which the highest practical results unwittingly follow from such investigations—made in abstract inquiry, the only end of which was thorough knowledge of the subject in all its scientific aspects and relations. This study of the strata underlying the Channel—an almost perfect example of close and careful reasoning on physical facts—was now brought forward to enlighten the projectors of a tunnel between England and France
