May 5, 1881] 



NA TURE 



15 



In the same way let black represent sand strata, and let 

 red represent succession in such strata ; then the sand- 

 stones will be represented by browns, the oldest being the 

 blackest, and the newest the reddest brown. 



3. Let igneous rocks be represented by a general colour, 

 as 7-ed, and let any order which obtains among them (suc- 

 cession, for example, if succession can be traced) be 

 marked by doses of another colour, as yellow ; then the 

 igneous rocks will be all red or orange, the newest being 

 the yellowest. 



4. Let other differences (as mineralogical differences) 

 be represented by other means, as by hatching. Thus 

 granite and quartz rock, if contemporaneous, may be 

 marked by red with the addition of lines — 



According to these principles the English strata would be 

 represented by the following colours, which may thus 

 be denoted by letters ; let Red, Yellow, Blue, Black, be 

 marked by R, Y, B, A, and let mi.xtures be represented 

 by combinations of the letters. Then we have — 



Orani^e, R R R Y, R R Y, R Y, R Y Y, R Y Y Y. 



Grcch, Y Y Y B, Y Y B, Y B, Y B B, Y B B B. 



Purple, B B B R, B B R, B R, B R R, B R R R. 



Broiun, A R R R, A R R, A R, R A A, R A A A. 



Unstratified rocks (primary), R. 



„ „ (trap), RRY, RY, RYY, &c. 



Clay slate, B R. 



Oldest limestone, B, B B B Y, B B Y. 



Oldest sandstone, A, A A A R, A A R. 



Secondary limestone (Mountain), B Y. 



New red sandstone ,, A R. 



Oolites „ BY Y, B Y Y Y. 



Green sand „ A R R. 



Chalk „ B Y Y Y Y. 



Observations : — I. The method here proposed would 

 answer the objects above stated, for the material and 

 order of succession are marked by their proper colours ; 

 and the sands, clays, and limestones which occur near 

 each other would be very distinct. Thus the green sand 

 is reddish brown (A R R) and the chalk is yellow green 

 (B Y Y Y Y). 



2. Perhaps it may appear an inconvenience that con- 

 tiguous members of a formation of the same material are 

 proximate shades of the same colour : thus the oolite 

 beds would be successive shades of green (B Y Y, 

 B Y Y Y), and might be difficult to distinguish. I answer, 

 that the beds themselves are often difficult to distinguish, 

 so that our language is most indistinct when our know- 

 ledge is most indistinct ; again, that the inconvenience, 

 when it is one, may be remedied by marking or hatching 

 those strata ; again, that no systematic method can be 

 devised which will not be open to this objection. 



3. The above principles being adopted, the whole range 

 of the colours, as modified by the succession-colour, might 

 be different according to the different object of the geo- 

 logist. Thus if he had to exhibit the whole geology of 

 England, all limestones whatever must come in between 

 B and Y (Blue and Yellow). But if he take the second- 

 ary period only, he may use all the possible shades of 

 green for members of that part of the series alone, and 

 may thus make his terms more numerous. 



4. If the -tvhole range of the succession-colour be em- 

 ployed and exhausted on a part only of the geological 

 series of strata, the strata which occur beyond this part 

 will, in the scale used on such occasions, be without 

 representative colours. This is an inevitable evil. We 

 cannot combine the extremes of detail and generality. 



If we use all our means in expressing a part, we must for 

 the time omit to express the remainder. We must do 

 this when our purpose requires and justifies it. 



5. When we use all our colours for part of the geologi- 

 cal series, we still preserve the principles above proposed 

 and the advantages which they secure, namely, that the 

 material and the succession are both exhibited in an 

 intelligible way without reference to the index. 



6. If we thus make a part of the geological succession 

 to occupy the whole power of our successive colour, we 

 have different colours from those which we have when we 

 represent the whole succession. The partial map has a 

 different index from the general one. This is a serious 

 evil, and must not be incurred without strong necessity. 



7. It may be mentioned as an advantage of the pro- 

 posed notation that many of the colours which are used in 

 it agree very nearly with colours commonly used : as red 

 for granite, blue for older limestones, yellow, or yellow- 

 green for chalk, brown for some sandstones, purple for 

 clays. The main novelties are that the oolites are green, 

 and the coal-fields not black ; but as to the latter point, 

 query, whether a coal stratum be a proper geological 

 distinction.'' If the coal-measures be sand or clay beds, 

 they should be brown or purple, according to the material 

 which is taken as characteristic. 



In a given case we may have to determine the question 

 above suggested, whether we should employ the whole 

 range of our succession colours on a limited geological 

 period, as, for example, the transition-period. In order 

 to decide this consider what you want. How many lime- 

 stones have you? How many sandstones, how many 

 clay-rocks, which are to be distinguished .' If the oldest 

 limestone be pure blue, and mountain limestone pure 

 green (B Y), we can easily interpose three or four lime- 

 stones, as (B B B B Y, B B B Y, B B Y) ; is this a suffi- 

 cient number of terms for you? and so of the rest. 



Summary. — Let there be in all cases a material colour 

 and a succession colour, namely — 



Succession. 



Y ... (Green) 

 R ... (Brown) 

 B ... (Purple) 



Y ... (Orange) 



The latter two lines lead to no confusion, for though R in 

 the clays indicates the material, it is never to be used 

 without B, and R in igneous rocks is never used with B. 



It may be observed that in the preceding scheme I 

 have not exhausted the power of colour, for I have not 

 used either the combinations of black with blue or of 

 black with yellozv, or the combination of three simple 

 colours. W. W. 



Dublin, August 17, 1835 



NOTES 



We are glad to learn that the Italian Governraent ha^ decided 

 on having a deep-sea expedition in the course of this summer to 

 explore the Mediterranean. The necessary arrangements are 

 now being made by Prof. Giglioli, the eminent zoologist, at 

 Florence, who will take charge of the biological part of the 

 work. Capt. Magnaghi will be intrusted with the physical part 

 of the work, as well as with the command of the vessel. The 

 scientific results may be expected to be of especial interest, 

 because nothing has been done to explore the depths of the 

 Mediterranean beyond the short cruie in H.M.S. Porcupine in 

 1870. 



Prof. Tvnd.^ll has written to the Times of yesterday a 

 letter of great intere^it on the attitude of the late Mr. Carlyle 

 towards modern science, which it has been taken for granted 

 was purely hostile. But according to Prof. Tyndall, not only 

 was Mr. Carlyle deeply interested in s 5me of the latest researches 

 of science, but he took great and successful pains to understand 



