ON INCREDULITY WITH RESPECT TO GEOLOGICAL FACTS. 57 
channel; we look at another and it is crossed in two or three 
directions by tracks apparently of birds; but when we ascribe 
these to the same cause you disbelieve it—why? Why does the 
impression of a foot on sand signify that an animal has walked 
over it, while the same impression on stone signifies nothing ? 
Well, the hardness of the material puzzles you. Now listen 
again. Suppose that your wayside channel, down which the rain 
sent a miniature torrent, was filled thereby with clay instead of 
sand—it is immaterial which, but we say clay to make the 
illustration more evident—and that the same impressions were 
made upon it, waves, ridges, hollows, footmarks ; suppose that it 
remained undisturbed by any agency whatever, under a hot July 
sun for a week, the identical marks would still remain, though 
they are on a harder surface; is there any reason now to doubt 
their cause ? What then if it lay undisturbed for many hundreds 
or thousands of years—or what if, when it was partially hardened, 
fresh layers of sand or clay were thrown down, and all the little 
hollows filled up, and then many ages elapsed and it was hardened 
into stone? Would it not easily split in the direction of the 
plane of all the markings, and exhibit those markings almost as 
distinctly as at first? You see clearly that the thing is not such 
an impossibility—that there is, at any rate, some probability in it. 
Look at this mass of shells I have brought from Lane End, it is 
almost as hard as iron ; but when I took it from the ground it was 
soft clay, and would scarcely hold its own weight together; am I 
not warranted in concluding that these shells once contained 
animals? If they did. I know from the character of the shells, 
that they were marine animals; if so may I not conclude, either 
that they have been brought from the now distant sea and buried 
here, or that the sea itself was once here, and that here they lived 
anddied? The former conclusion is too unlikely to be entertained 
fora moment. As regards our own chalk hills there is not much 
difficulty if the foregoing conclusions are accepted. Different 
rivers and seas carry away different kinds of mud or sediment 
with them, and, therefore, when it is deposited, different kinds of 
stone are formed; the sea washing the chalk cliffs of Dover, 
