746 REPORTS ON THE STATE OF SCIENCE. 



drifting sand. The conventional use of the word rock in geology has been so 

 widely adopted that objection to it may appear pedantic. Rosenbusch, 11 how- 

 ever, has defined Rocks as ' the geologically independent constituents, of more 

 or less constant chemical and mineralogical composition, of which the firm 

 (feste) crust of our earth is built.' Hence such definitions as that in my 

 ' Structural Geography ' (p. 21) of rocks as the firm coherent masses which form 

 the main part of the lithosphere may shelter behind the high authority of 

 Rosenbusch. 



Reference to the paradox of calling clay and sand rocks reminds me that the 

 word clay is now used in two very different senses in two sections of geology. 

 In mineralogy the clays are a group of mineral species which are hydrous sili- 

 cates of alumina. To the merchant, the farmer, and the economic geologist the 

 essential quality of clay depends on texture and not on chemical composition. 

 The word clay appears to be based on the same root as clog and cleave, while the 

 Russian glina and the Greek 7A1C* connect it with glue and glutin. The root 

 of the word clearly refers to the adhesiveness which clay owes to its plasticity. 



The essential property of clay is that it becomes plastic when wet. In 

 England this property is chiefly found in material which, being formed from 

 decomposed felspars, is a hydrous silicate of alumina ; but other common materials 

 have the same property, if ground to the requisite fineness. Quartz-flour is a 

 common clay-forming material in many parts of the world, and much of the 

 material called clay by the farmer is pure silica. Hence the definition of economic 

 and agricultural geologists that clay is earthy material, which is plastic when wet 

 because its particles are no more than 0005 mm. in diameter, is a more common- 

 sense definition than any based on chemical composition. '- 



If a name be wanted to distinguish clays which are silicate of alumina 

 from clays of different composition, then a new name should be invented, in- 

 stead of adopting a definition which refuses to accept as clay the slime of the 

 quartz-miner, much of the Scottish boulder-clay, and any one of the nine 

 brick-clays in the table of brick-clay analyses given by Ries. 13 



I have referred to a few instances to illustrate the frequent misappropria- 

 tion of current terms by various branches of science, in the hope that the mem- 

 bers of the Corresponding Societies will use their influence to discourage this 

 practice. It should be remembered, however, that there are many cases in which 

 it is a wise policy to transform a current popular term. It may be even justifiable, 

 as in the case of minium and cinnabar, to use a word with the very opposite 

 of its original meaning. A term may be adopted and redefined where, as in the 

 cases of fish and worm, the popular meaning involves a wrong idea which it is 

 advisable to correct, or overlooks a distinction which is practically important. 

 Change and growth in nomenclature must be allowed. A dead language is very 

 good for fixed ideas; but rigid adherence to original meanings is a bondage 

 from which it is to be hoped scientific terminology may be always free. It is 

 useless to suggest rules as to when popular terms may be revised ; each case 

 should be judged on its merits. 



The casual adoption of current words with new meanings is often an attempt 

 to secure specious simplicity at the price of subsequent confusion. Deissmann's 

 recent book, 'Light from the Ancient East' (1910), calls attention to the mis- 

 conceptions that have similarly arisen in theology, for he urges that words used 

 in the New Testament are now understood in what the authors of that volume 

 would decidedly call a non-natural sense. The idea that science is being driven 

 into an intellectual wilderness owing to it's technical terminology is an idle 

 bogey. Reference to the sporting or business columns of any daily paper will 

 show that all specialised pursuits have their own special language. The language 

 of golf is as technical as that of geology, and I venture to urge that science 



II H. Rosenbusch, Elements der Gesteinslehre, Stuttgart, 1910, third edit., p. 1. 



,! Ries' definition, ' Clay is the term applied to those earthy materials occurring 

 in Nature whose most prominent property is that of plasticity when wet ' (H. Ries, 

 Clays : Their Occurrence, Properties, and Uses, with especial reference to those of the 

 United States, 1906, p. 1), is an example of those based on texture and not on 

 composition. 



13 H. Ries, ibid., p. 185. 



