﻿Geological Society. 10(51 



point will, on the average, be reached in, at most, a year, and, at 

 the quickest, may be of such rapidity as to be analogous to a 

 separate explosion for each earthquake. The possibility of so 

 rapid a growth of strain being due to tectonic processes, as 

 ordinarily understood, is considered and rejected, so that the 

 changes by which the strain is produced must be referred to the 

 material below the crust. Recent researches on the change of 

 bulk, resulting from a change in the mineral aggregation of the 

 same material, are referred to, as indicating one means by which 

 the required effect may be brought about ; and, without restricting 

 the possibilities of other unknown processes, the results are 

 summarized as indicating that the cause of the great majority of 

 earthquakes is a rapid growth of strain, and that the production 

 of this strain must be referred to changes which take place in the 

 material underlying the outer crust of solid rock, which is directly 

 accessible to geological observation. 



March 22nd.— Prof. A. C. Seward, Sc.D., F.R.S., President, 

 in the Chair. 



Sir Charles John Holmes, Director of the National Gallery, 

 proceeded to deliver a lecture on 'Leonardo da Vinci as a 

 Geologist.' The Lecturer began by referring to the growth in 

 recent years of Leonardo's reputation as a man of science. This 

 rapid growth led recently to a reaction, and it was now not 

 infrequently stated that Leonardo's scientific discoveries were in 

 the nature of fortunate guess-work, and were neither proved nor 

 accompanied by experimental research. In view of this attitude, 

 the Lecturer felt that he could not present any statement of 

 Leonardo's discoveries to a scientific body, such as the Geological 

 Society, except in the form of extracts from Leonardo's own 

 writings, which would enable them to judge for themselves 

 whether his scientific reputation was firmly founded or not. 



Reading extracts from the translations made by Mr. McCurdy 

 and Dr. Ric liter, the Lecturer pointed out how Leonardo was 

 really the first to have a large and accurate conception of the 

 causes underlying the physical configuration of the Earth. His 

 studies of aqueous erosion, of the formation of alluvial plains, of 

 the process of fossilization, and of the nature of stratification, led 

 him to a logical conviction of the immensity of geological time, 

 and were so far in advance of the dogmatic thought of his age, 

 that they exposed Leonardo to the charge of atheism. There can 

 be no doubt whatever, that if he had not confided these dis- 

 coveries to the almost undecipherable script of his note-books, and 

 kept them hidden there, he would have been one of the first and 

 most notable of the martyrs of science. 



Caution thus compelled him to work in isolation, and to keep 

 his results concealed : he had no scientific instruments, no corre- 

 spondents to furnish him with observations on geological conditions 

 elsewhere ; yet his grasp of the physical history of the portions of" 



