2 BRITISH GRAPTOLITES. 



fac-similes of these fossils could be reproduced in the printing-press. Many 

 of the best figures yet published are more or less unconsciously idealised or 

 inadequate. How impossible it has been to feel confident that the figures and 

 descriptions give an adequate transcript of the facts, even when both author antl 

 artist are of the best and most trustworthy, needs only one illustration. Several 

 of the forms described and figured in the epoch-making work of Barrande on 

 the ' Graptolites de la Boheme ' have been differently interpreted by almost 

 every field geologist and palaeontologist who has used the book. 



To meet this difficulty it was obviously necessary to give such figures of 

 the fossils themselves — by mechanical means if j)ossible — as should agree with 

 the originals in all respects, showing their imperfections as well as their perfec- 

 tions, that the reader might be in a position to judge of the fidelity of the 

 descriptions by the figures themselves, and might also be able, should the need 

 arise, to identify the actual fossil or type specimen represented on the plates. 



The vast majority of our British Graptolites are preserved as thin, shining 

 films or markings upon the surface of l)lack shales. They can be seen, in most 

 cases, only by reflected light, so that illustration by direct photography is out of 

 the question. Again, the specific characters of these fossils depend upon markings, 

 features, and measurements of almost microscopic minuteness, and no figure can 

 be regarded as satisfactory unless these details can be identified upon it by 

 means of an ordinary hand-lens. And, as the illustrations are required for con- 

 stant comparison with ordinary specimens obtained in the field, it is necessary 

 that they shall be figured of the natural size. 



After some years of experimenting it was found that the best plan of 

 obtaining satisfactory fac-similes of these fossils was to draw them by means of 

 the camera lucida attached to a special microscope constructed for the purpose. 

 On this microscope the slate carrying the fossil is attached to a large stage, having 

 a universal joint and a travel of several inches. The light can be so adjusted 

 that the amount of distortion due to the obliquity of the stage is small, and mav 

 generally be neglected. 



The usual method of procedure is to draw each fossil in l)lack crayon to a scale 

 of five times the natural size, so that all visible details can be inserted. When 

 finished, the drawing, which has been tinted with a grey tone, is reduced by means 

 of photography to the natural size. 



When such drawings are photographed as silver prints, the details come out 

 with exquisite sharpness. Unfortunately, however, no mechanical process suitable 

 for the printing-press has yet been invented in which the grain of the background 

 carrying the printei''s ink is sufficiently fine to allow of the sharp reproduction of 

 all this detail. By far the best process among those which I have tested is 

 collotype, which is consequently the one adopted in the present Avork. The 

 collotype plates which illustrate this Monograph are hj Messrs. Bemrose, of Derby, 



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