NEWTON : ON COLOEATION IN FOSSIL SHELLS. 281 



to a number of Carboniferous shells which showed unmistakable 

 pattern-markings derived from original colour, Forbes was of opinion 

 that they were characteristic of molluscs which had lived in a less 

 depth of water than 50 fathoms, and he consequently considered that 

 the Carboniferous Limestone deposit of most regions must have been 

 a shallow- water formation. 



These views were subsequently supported by Lyell,' S. P. Woodward,^ 

 and Paul Fischer,^ besides being generally accepted at the present day. 

 Gwyn Jeffreys,* however, disbelieved in this argument on the ground 

 that some vividly coloured shells had been obtained from depths 

 varying from 60 to 11 8 fathoms, including such forms as Tapea virc/inea, 

 Venus ovata, and Trochtin ziziphinus ; and he was of opinion that " the 

 extent to which light penetrates into the abysses of the ocean, as well 

 as the mode of its transmission, does not seem to be known." 



Examples of fossil shells exhibiting colour - markings are com- 

 paratively rare from the fact that chemical changes, erosion, and a 

 variety of other causes operating during the process of fossilization, 

 have altered to a large extent the constituent elements of the shell- 

 structure. Whatever colours may be now apparent in such fossils 

 they do not necessarily represent what was there in the life of the 

 mollusc, but rather a replacement of the same has most probably 

 resulted by subsequent colouring mediums, generated by the agencies 

 just mentioned, which were pregnant at tlie time of the consolidation 

 of the strata in which the shells are found. Such markings on fossil 

 shells are, therefore, of interest as denoting the position and general 

 arrangement of the colour-patterns that were characteristic of the 

 mollusc during life. 



Shell colour-markings are by no means superficial, as can be tested 

 by examining a modern Circe, the valve-margins of which show that 

 the pigment lines are sunken to about half a millimetre in depth. 

 Thus it is that in fossil shells the colour-patterns are often preserved 

 as finely indented lines, bands, spots, etc., which are slightly below 

 the ordinary level of the surface. 



According to Fischer's "Manuel" (p. 27), melanism and albinism 

 are phenomena well known among the Mollusca. For instance, such 

 genera as Trochus, Turho, Chiton, Fissurella, Mitra, Turritella, etc., 

 found off the west coast of South America, have a black exterior ; 

 whilst Monterosato ^ has noticed pronounced albinism existing amongst 

 marine shells which live in sponges found at Tunis in Northern Africa, 

 35 albino forms having been observed out of a total of 120 species. 



Colour remains are also met with in other organisms that are found 

 in the fossil state. Among the Brachiopoda, for instance, may be 

 mentioned the radiating stripes which are frequently preserved on the 



A Manual of Elementary Geology," 5th ed. (1855), p. 410. 

 A Manual of the Mollusca," 1851, p. 46. 

 Manuel de Conchyliologie," 1880, fasc. i, p. 26. 

 British Conchology," vol. i (1862), p. xlix. 



Notizie intoruo ad alcune conchiglie deUe coste d'Africa " : Bull. Soc. Malac. 

 Ital., vol. V (1880), pp. 213-233. 



