76 
supplied me with several specimens of the fossils from the 
limestone quarry at Kilwinning, which are very different 
from those I previously examined, and which throw more 
light on the changes which siliceous fossils may undergo, I 
beg to give an account of them to the Society, One piece 
of limestone simply contained (instead of rods) a number of 
cylindrical holes where the rods had lain. In Fig. I, which 
is a woodcut from a photograph, are seen these cylindrical 
holes which plainly show that the rods have been dissolved 
away. The solvent must have been a strong calcareous or 
other alkaline solution, as the calcareous fossils are not in 
the least disfigured. In. Fig. 2 we see a beautifully pre- 
served sample ofFenestella, and we know that a very slight 
