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ON THE GOTHAM MARBLE 
bubble could support such thick masses, often an inch 
high, and as soon as it burst the hummock would collapse. 
C. A New Theory of the Gotham Marble. 
I. I believe the Gotham Marble to have had a Chemical 
Origin, for the following reasons. 
i. The texture and composition of the stone. From these, 
Thompson also deduces a chemical origin. The purity, 
the freedom from mud, and the uniformly grained very 
finely crystalline structure all suggest this. Other chemi- 
cally formed bodies, e.g. urinary calculi, present just the 
same microscopical appearance. 
ii. The nature of the slabs, of the typical texture, in False 
Gotham Marble. These were obviously once horizontal, 
in the midst of a calcareous ooze, and yet were so dry and 
brittle that when disturbed they broke up rather than 
bend. Only in one locality is there even slight bending. 
Now it is well known that a crystalline or chemical deposit 
hardens rapidly ; not so a product of drying. Moreover, 
in the wet ooze dried layers would soften ; only chemically 
formed ones could remain brittle. 
iii. The presence of spherical concentrically banded con- 
cretions of typical texture in the same horizon, often showing 
“ hedge-structure ” and even found embedded in the False 
Gotham Marble. It is well recognized that spherical con- 
cretions must be chemical. The imitations of Gotham 
Marble from the Purbeck and Oolite also seem to be con- 
cretionary. Every v/riter on the subject has acknowledged 
how like the “ canopy ” is to a concretion. 
Sometimes these concretions enclose pale bluish-white 
baryto-celestine in large crystals, which has evidently 
crystallized out subsequently in situ. 
iv. The Analogy of Urinary Calculi, especially those 
formed of calcium oxalate (Fig. 5). These present : — 
