The powder has been analysed for me by Mr.T.
Reeks; it consists of sulphates and muriates both of lime and soda, with very little carbonate of lime.

It is known that common salt and carbonate of lime left in a mass for some time together partly decompose each other; though this does not happen with small quantities in solution.

As the half-decomposed shells in the lower parts are associated with much common salt, together with some of the saline substances composing the upper saline layer, and as these shells are corroded and decayed in a remarkable manner, I strongly suspect that this double decomposition has here taken place.

The resultant salts, however, ought to be carbonate of soda and muriate of lime, the latter is present, but not the carbonate of soda.

Hence I am led to imagine that by some unexplained means the carbonate of soda becomes changed into the sulphate.