Correspondence—Rev. W. Downes. 431 
that the fossils are “not always exactly coincident with the cleavage,” 
and one of his specimens illustrated this. 
I repeat, therefore, that there can be no question whatever as to 
the fact. I then set myself to work to account for it. 
The first question which I proposed to myself was this, “How can 
fossils be deposited otherwise than on a plane of bedding?” And 
it appears to me to be no very difficult one to answer. Various 
exceptional circumstances might account for them in isolated cases ; 
but for a common cause affecting a wide area of rock, we need only 
suppose tranquil conditions of deposit. Where there is absolutely 
no current and a soft oozy bed, shells, etc., would fall with the major 
axis in a perpendicular position, and in such a position they might 
probably remain. For some reason or other Turrilites is found 
“ invariably at right angles to the stratification,” in the Chalk-marl of 
the South of England. This is due, perhaps, in the first instance, to 
the fact that it is a Cephalopod; but it is evident that, if a current 
existed at the sea-bottom, the fossil would assume a horizontal 
position immediately after the death of the animal. That it has not 
done so proves tranquil conditions of deposit. 
If we apply the same reasoning toa silty deposit, which has since 
been altered into slate, it will fully account for such organisms as 
sea-weeds and Graptolites being found inclined at a high angle to the 
bedding. Who ever saw a seaweed or Sertularian in a perfectly 
horizontal position in sea-water, unless perhaps in the tide-race ? 
In still water the comparative buoyancy of their several parts would 
determine their position. And in such a position the silt would fall 
around them and entomb them. 
The second question which occurred to me, and which is by no 
means so easy to answer satisfactorily, is this—‘‘How came the 
fossils to be revealed in so many instances upon a superinduced 
structure like cleavage?” “How is it that the cleavage plane 
should happen to be exactly that in which those fossils lie?” I can 
énly suppose that the slate rock at Carrick-on-Suir is in reality 
densely crowded with such organisms as Graptolites and Fucoids, a 
small per-centage of which are revealed by the cleavage. If the large 
majority of the organic remains which have been deposited there are 
deposited upon the ‘planes of bedding, they are for ever lost 
to science, for the rock never divides along the bedding planes. 
The cleavage destroys all traces of the delicate impressions, except 
those (comparatively few) which happen to have been deposited 
exactly or very nearly along the lines which the cleavage afterwards 
followed. But we should expect to find some half revealed by lying 
imperfectly upon the cleavage plane, and this is exactly what we do 
find. 
In some cases, in irregularly-cracked shales, I have seen cracks 
diverted, as to their direction, by the presence of a fossil, and 
perhaps the very selection of the divisional plane, dependent, as it 
would be, upon the line of least cohesion, may be determined here 
1 Science Gossip, 1879, pp. 204-4. 
