54Q 



NATURE 



[October ig, 1911 



zoologist is only a return to the primary meaning of 

 the word. 



mistry supplies an excellent illustration of the justifi- 



able adoption of an old term with a revised meaning. 



ent is used in its later classical meaning, and Chaucer 



in 1386 shows that it was used in Early English in a 



similar sense. He says in the Frere's Tale (line 206) : — 



Its modern chemical use means the resurrection of the 

 word element to a new period of usefulness. 



The chemical adoption of the terms metal and non-metal 

 for the two classes of elements is, on the other hand, an 

 example of the inconvenience that results when a new 

 definition is only approximately coincident with a well- 

 established current meaning. The word metal appears to 

 be derived from the Greek ^aaXKov. connected with 

 neraWdui, " to seek after," through the Latin metallum, 

 a mine or quarry, or substance obtained by minint;. Hence 

 road metal for stone is correct. 



By the time of Johnson the word metal was usually 

 restricted to those products from mines which have metallic 

 as distinct from earthy or stony properties. Johnson's 

 definition — " We understand by the term metal a firm, 

 heavy, and hard substance, opake, fusible by fire, and 

 concreting again when cold into a solid body such as it 

 was before, which is malleable under the hammer, and is 

 of a bright, glossy, and glittering substance where newly 

 cut or broken " — states the general idea of a metal. 



The chemical adoption of the word for the larger of the 

 two classes of elements has resulted in the use of the word 

 metal in science with two contradictory senses ; thus in 

 elementary geology the word is used with its chemical 

 meaning ; but in economic geology metal is used in its 

 commercial sense. 



Sodium and potassium are therefore metals in elementary 

 geology and academic mineralogy ; but they are not metals 

 in advanced economic geology. This double use of the 

 word is an occasional source of confusion and discounts 

 any good advice that may be given to students as to 

 precision in the use of terms. It is perhaps too late to 

 change, but it would have been better if the chemists had 

 adopted technical terms for the two groups of elements 

 instead of applying the term metal to a material so unlike 

 the ordinary idea of a metal as is sodium. 



Geology has been a particularly flagrant sinner in the 

 misuse of popular terms. Its nornencfature has not only 

 unconsciously absorbed and modified many English words, 

 but committees "I experts have deliberately committed such 

 wholesale piracy that our language has been left bankrupt 

 in some departments. Thus terms are needed in strati- 

 graphy for the various subdivisions of the sedimentary 

 rocks and for the lengths of time occupied in their deposi- 

 tion. The International Geological Congress proposed the 

 following series of terms, beginning ~ with the larger 

 divisions : — 



Group. 

 System. 

 Series. 

 Stage. 



Equivalent T 

 Era. 

 Period. 

 Epoch. 



Although a systematic nomenclature would be very 

 useful, this scheme has not been generally adopted; and I 

 think the reason is that, by assigning definite meanings to 

 ■'II the indefinite terms available, there is nothing left for 

 use in nn indefinite s.nse. Thus a number of beds, which 

 together may be either more or less than a subdivision 

 of a system, cannot be called a series without risk of 

 misunderstanding. All the above eight terms are required 

 for use in geology with their current English meanings. 

 The scheme proposed by the International Geological Con- 

 rolves u-.ing these words sometimes in a technical 

 and sometimes in a non-technical sense. In literature the 

 difficulty may be overcome by printing the words with 

 1 tpital letters when they are used as the names of definite 

 'i 11 1 impossible in speech. The principle 

 recommended by the International Geological Congress was 

 excellent, Inn the scheme proposed has proved impracticable 

 owing t 1 ition of old words to new things. 



0. 2 I 90, VOL. 87] 



Buckman adopted a sounder policy when he introduced 

 the term Hemera for the time equivalent to a zone. 



Geologists have adopted some common words with 

 meanings which render geological phraseology unintelli- 

 gible or even ludicrous to the, man who has not been 

 warned that they require special interpretation. Thus the 

 need in elementary teaching for emphasising the differ* 

 between mineral species and mineral aggregates has led 

 to the frequent use of the term mineral as an abbreviation 

 for mineral species. Some authors have been led by this 

 practice to deny that mineral aggregates are minerals, and 

 therefore assert that coal, most iron ores, oil shale, mineral 

 oil, &c, are not minerals. According to that view the 

 mineral industry has little concern with minerals; and the 

 mineral resources of the British Isles, which are generallj 

 regarded as extensive, are reduced according to this nomen- 

 clature to practically nothing. 



Another triumph of dauntless logic is the use of the word 

 rock. It is no doubt convenient, when speaking of the 

 crust of the earth, to have one term to cover all its 

 materials ; and rock is used in this way just as the dust in 

 the atmosphere and the salts in the sea may be included 

 with the air and the water. Hence has arisen the 

 geological convention of calling any large constituent of 

 the earth's crust a rock, quite regardless of the cohesion of 

 its particles. <■. H. Kinahan, for example, in his "A 

 Handy Book of Rock Names " (1873), says, " Thus loose 

 sand, clay, peat, and even vegetable mould, geologically 

 speaking, are rocks " (p. 1) ; and on p. 131 he includes ice 

 among rocks. 



Now this use of the term ignores the very essence of the 

 popular idea of a rock. The term appears to be derived 

 from the same word as crag, and the essential quality of a 

 rock is firmness. The parable of the man who built his 

 house upon a rock would need to be retranslated, and 

 Shakespeare's " He's the rock, the oak not to be wind- 

 shaken," 1 loses its meaning if rock may be loose, drifting 

 sand. The conventional use of the word rock in geology 

 has been so widely adopted that objection to it may appear 

 pedantic. Rosenbusch, 3 however, 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 

 silicate's of alumina. To the merchant, the farmer, and 

 the economic geologist the essential quality of clay de nd 

 on texture and not on chemical composition. The ' 1 d 

 clay appears to be based on the same root as clog and 

 cleave, while the Russian glina and the Greek 7*10 conm 1 t 

 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 ciav by the farmer is pure silica. Hence the defim- 

 tion of economic and agricultural geologists that clay is 

 earthy material, which is plastic when wet, its particles 

 being no more than 0-05 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, 



1 Coriolanus, v. 1, 117. Cf. also Zangwill -" Feeling solid-based upon 

 eternal rock." 



2 U. Ro«enbusch, " Elemente der Gesteinslehre," Stuttgart, 1910, third. 



s Ries°s" 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, ProDerties, 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. 



