POPULAR SCIENCE 599 



deposit has been scratched by another rock by means of pressure 

 brought into play by moving ice, or by earth movements of one 

 kind or another. 



The scratches themselves, however, provide a very profit- 

 able field of study. If an extensive series of striated flints is 

 put out for examination it will almost certainly be noticed that 

 some of them, though thin, nevertheless exhibit upon one or 

 other of their surfaces wide and deep striae. To those who have 

 not made a close study of this subject it would appear that 

 these striae were imposed as we now see them, by the initial 

 impingement of the rock which passed over the flint surface, 

 and it will also probably be assumed that a great amount of 

 pressure was exerted to produce such a result as is observable. 

 Most people are aware that flint is a very hard substance, 1 and 

 these conclusions therefore appear reasonable and sound ; 

 but in reality they are quite unsound. When the author com- 

 menced his investigation of striated flints he was at once 

 struck with the remarkable fact that comparatively thin flakes 

 of flint should have stood, without breaking, the great amount 

 of pressure to which they must have been subjected if the deep 

 strise present upon them were imprinted by the initial impinge- 

 ment of the agent of striation, and this feeling of astonishment 

 was increased by the knowledge, gained in experiments carried 

 out in another investigation, that the soundest flint nodules will 

 disintegrate under a quite moderate amount of pressure. He 

 concluded, therefore, that the deep strise developed upon the 

 flakes of flint are not now in their original condition, but have 

 become accentuated and altered since they were first imprinted. 

 The difficulty was to find out how and why this accentuation 

 and alteration had come about, and an examination was com- 

 menced therefore of several hundreds of scratched flints from 

 various deposits, and from the present land surface. 



This examination demonstrated clearly that while some of 

 the specimens showed wide and deep otriae or grooves on their 

 surfaces, others exhibited lines of shattering, composed of very 

 thin and minute plates of flint, instead of the well-marked 

 grooves (fig. 1). Further specimens again exhibited a com- 



1 Reinhard Brauns in his book, TJie Mineral Kingdom, p. 51, gives Moh's 

 scale of hardness of minerals, in which quartz is quoted as being the fourth hardest 

 mineral. Bristow, in his Glossary of Mineralogy, p. 140, states that flint is 

 "slightly harder than common quartz, which it scratches." 



