Cornish and Kendall—Cualeareous Organisms. 69 
a passage which has reference to the Portland Oolite. It will be 
noticed that Mr. Sorby’s conjectures are borne out in detail by our 
experiments. The passage is as follows: ‘ Where the deposit has 
taken place in a current, they (the aragonite shells) are more or less 
completely absent, probably because they had become tender by 
decomposition and were broken up before final deposition. Under 
similar circumstances the calcite shells have resisted complete disin- 
tegration and still show the original structure.” 
At Walton-on-the-Naze the uppermost beds of fossiliferous Red 
Crag contain very few calcite shells and immense numbers of 
aragonite shells. The latter are as a rule greatly decorticated and 
often quite pulverulent. The overlying bed formerly referred to as 
“Unproductive Sands” does not as a rule contain any shells, but 
thin lenticular patches of greatly decomposed fragments of shells 
occur, the species of which could sometimes, though rarely, be 
determined. This, and the circumstance that locally pipes of 
unproductive sand descend into the fossiliferous beds below, show 
conclusively that this was a case of decalcification. A prior obser- 
vation by Mr. Whitaker (Q.J.G.S. vol. xxxiii.) led him to the same 
conclusion. 
In a Coralline Crag-pit opposite Mr. Chaplin’s farm-house on the 
road from Dullingham to Sudbourne, very loose sand containing 
only decomposed calcite shells can be seen to pass up into a loose 
sandy bed destitute of fossils. 
Near Sudbourne Church a similar sand occurs, which can be 
recognised as decalcified crag, by the circumstance that a large per- 
centage of the sand grains are coprolitic, a character which 
distinguishes the Red and Coralline Crag from all other deposits. 
In the classical pit in Sudbourne Church Walks (Mrs. Rackham’s), 
where the superposition of Red upon Coralline Crag can be observed, 
the Coralline Crag has suffered the removal of its aragonite shells, 
while the overlying Red Crag contains a profusion of organisms of 
aragonite constitution, a fact which appears to indicate that, previously 
to the deposition of the Red, the Coralline Crag had stood above the 
sea-level and had undergone submergence. 
Part II. 
As stated by Mr. Sorby, the true mineralogical character of any 
calcareous organism is best indicated by the specific gravity. This 
was determined by Mr. Sorby from the powdered substance. We 
were desirous, however, to ascertain if the destruction of the specimens 
could be avoided ; and the following numbers from our determinations 
by the method of suspension show that in many cases at least it is 
not necessary to sacrifice the specimen. In the case of univalve 
shells, however, it is sometimes necessary to break into the whorls. 
Where a recent specimen has a thick epidermis, this must be removed 
by caustic soda. 
The observations which follow were made in following out the 
indications obtained :—1. from the known inferior stability of arago- 
nite fossils; 2. from the rule which appeared to hold with regard 
