58 
Proceedings of Royal Society of Edinburgh. [sess. 
annelid working in rocks. In the first place, the tubes where 
exposed in transverse section, in undisturbed material, will be 
approximately circular. In the second place, when they are cut 
across, not at right angles, but obliquely to the path of the worm, the 
section will be more or less ovate. In the third place, the same 
effect will be produced when the material has been disturbed by 
shearing or slipping of the beds or laminae of deposit. Such 
movements, if not violent, will produce an elongation or pulling out 
of the cross section of the tubes, with resulting ovate forms. In the 
fourth place, where the movement of material has been great and 
effected under great pressure, the tubes will have been more or less 
completely crushed and flattened and distorted. In the fifth place, 
where the tube has been preserved at all, so as to show its original 
walls, those walls will very probably be traceable by a deposit or 
staining of oxide of iron, replacing the animal matter which origin- 
ally agglutinated the sand. In the sixth place, this feature will 
necessarily be very variable according to the greater or smaller 
quantity of iron in the sand or clay. In the seventh place, where 
the tube has been so far preserved as to present a cross section of 
the substance filling up the interior of it, there will be a visible 
difference between that substance and the material outside the tubes, 
corresponding to the difference which has resulted from the selec- 
tion by the worm of the finer from the coarser particles, and of the 
argillaceous particles from the purely silicious, because of their greater 
richness in digestible organic matter. In the eighth place, this 
selection of the finer clay particles by the worm, and the voidance of 
them in the tube behind it, would constitute a definite and probably 
a lasting difference in the mineral conditions of the whole space 
occupied by the path of the worm, which difference would be 
reproduced and perpetuated by the dirferent behaviour of different 
mineral substances under the processes of metamorphism — whatever 
these may have been. In the ninth place, as in all the surrounding 
country the silicious strata are in general sharply distinguished from 
the argillaceous beds, and as these last have been generally meta- 
morphosed into mica slates, with pure mica very highly developed 
in most of them, we should expect to find, as a necessity of the case, 
a corresponding development of mica and of micaceous particles in 
the inside of the worm tubes or along the lines of alteration and 
