LARGE BOULDER FOUND AT BRANKSOME. 163 



have been examined by Mr. William Whitaker, Dr. Hinde, and 

 the authorities at Jermyn Street. Mr. Whitaker writes : "I 

 took specimen and slide to Jermyn Street and got Dr. Teall to 

 look at them. He was struck with the great variety of the 

 quartz grains in size and shape (under microscope), and that 

 is not a sarsen character, the grains of these stones being fine. 

 I then went up to the petrologic department, and Mr. 

 Rhodes turned out a specimen which, under microscope, 

 was rather like yours, though differing to the eye. Curiously 

 enough, this was labelled ' Quartzite, Parkstone, 200ft. 

 gravel." 



After sending Mr. Whitaker the sarsen slide from Bridehead, 

 I heard from him as follows : " To-day I took them to Jermyn 

 Street, and showed them to Dr. Flett, petrologist to the 

 Geological Survey, and we compared them with some others. 

 Dr. Flett detected some differences between your rock and 

 grey wether-slides. In the latter the cementing material 

 is less in quantity and is largely secondary quartz ; that is, 

 quartz crystallised in the rock. In the former it is not so. 

 He would, therefore, class your boulder as approximating to 

 quartzite, and he concludes that it is not a greywether. 

 Both quartzite and greywethers vary very 

 much." 



Dr. March is not satisfied with this conclusion. He had 

 occasion, some years ago, to go into the subject of quartzites, 

 granitoids, and grits, and possesses micro-sections of Hasling- 

 den grit, Gannister grit, Gritstone from Lower Coal Measures, 

 Gritstone from Devon, and Silurian quartzite from Ireland, 

 Normandy, and Norway. All these show resemblances to, 

 but are easily distinguished from, our stone ; but on comparing 

 this with the Bridehead sarsen he writes : " These, I main- 

 tain, are fundamentally indistinguishable, though it is true 

 that one has more cement than the other ; but that is 

 unimportant. I think it is true that there is more secondary 

 quartz in the Branksome stone than in the Bridehead one, 

 but this must certainly vary in different specimens. It is 

 silicified Tertiary sand, and this sand is sometimes silicified 



