348 SECTIONAL TRANSACTIONS.— C. 



and further east. These gravels constitute an impersistent terrace between the levels 

 of Boyne Hill and Taplow terraces, and they are the only deposits in this district 

 which contain fresh and unrolled implements. They may therefore be taken as 

 a useful datum line. The higher or Boyne Hill gravels contain only much-rolled 

 specimens rather small in size and either sharp-rimmed ovate or bluntly pointed 

 in form. Moreover, they are very scarce and their original home has not yet been 

 discovered. Probably they were swept off an old land surface which has long since 

 disappeared. The implements in the Taplow gravels are always rolled, and obviously 

 derived from the Furze Piatt deposits, being only found in those localities where the ■ 

 latter are well developed. The above views are based on nearly forty years' close 

 observation of most of the excavations made in the district. 



Rev. Charles Overy. — The occurrence of Leytonian implements in the Taplow 

 Terrace near Maidenhead as derivatives is probably to be explained by the destruction 

 of the 135-ft. to 140-ft. terrace so well marked north of Reading, from which the 

 speaker has obtained many implements. 



The succession of plateau gravels at definite stages ranging from 350 feet above 

 river-level to the Handborough Terrace with glacial erratics is very distinctly marked 

 in the Oxford area, and includes a well-marked series at 200 feet above river-level 

 corresponding with Mr. Wooldridge's base level in the Lower Thames. 



7. Mr. S. S. BucKMAN. — Shotover Brickyard : the Age of the Clay above the 



Shotover Grit. 



8. Papers on Geological Technique and Research Methods (Mr. I. S. 



Double, Prof. W. T. Gordon, Prof. H. L. Hawkins, Dr. A. 

 Heard, Dr. E. Neaverson, Dr. H. Hamshaw Thomas, Mr. John 

 Walton, Dr. W. F. Whittard). 



Prof. W. T. Gordon. — The Preparation of Thin Rock-sections. 



^The origin of the idea of examining the internal structure of stony material by 

 means of thin sections is quite uncertain, and was probably a development from the 

 methods of early crystallographers, who prepared thin slices of minerals for optical 

 examination. For instance, we find Brewster, in 1817, making slices of amethyst 

 one-fiftieth of an inch thick for optical research. It is interesting to note that 

 lapidaries were employed in preparing such sections, and, as these operatives had 

 long been accustomed to prepare slices of agate and other materials for decorative 

 purposes, we cannot be surprised that much credit is deservedly given to them. When 

 the importance of the process was fuUy realised, it seems to have become impossible 

 to give the credit to anyone in particular, but the history of the method, so far as it 

 is known, is not without interest. The earliest publication describing the process of 

 manufacture was by Witham in 1831.^ He attributed his knowledge of the method to 

 Nicol, and certainly described Nicol's modification of Sanderson's method.'* An 

 enlarged work in 1833 does not contain this description, and on that account, as well 

 as for other reasons, Nicol seems to have become incensed at the work and also the 

 author. 



Nicol gave vent to his passion in a paper published in the ' Edinburgh New Philo- 

 sophical Journal,' ' and, though petulant in tone, the article is of some importance in 

 clearing up the vexed question about the origin of section-cutting. Nicol makes no 

 claim to have originated the idea, but states that the first ' in this quarter ' (Edinburgh) 

 to make thin sections of fossil plants was a lapidary, Sanderson by name^ — the man 

 also mentioned by Witham. Sanderson's method was to slice a piece from the 

 specimen and fix it down, by means of lapidary's cement, to a wood block, thereafter 

 smoothing and polishing the exposed surface. The cement was softened, the slice 

 reversed, and the under surface now rubbed down until it was considered suflSciently 

 thin for the purpose on hand. This surface also was polished, and, on re-melting the 



1 ' Observations on Fossil Vegetables.' Edin. 1831. 



2 ' The Internal Structure of Fossil Vegetables.' Edin. 1833. 



8 « Observations on the Structure of Recent and Fossil Coniferae.' Edin. New 

 Phil. Journal. 1834. 



