568 C. H. GORDON 
toothlike projections or columns projecting from the opposing sur- 
faces along a plane of fracture whereby the two parts of the stone 
are so intimately interlocked that often the slab will break more 
readily elsewhere than along the suture. 
The theory that they are due to differential compression in beds 
of soft calcareous sediments separated by a thin film of clay was 
first proposed by Quensted (1861) and adopted by Marsh (1867), 
Gumbel (1882), Rothpletz (1900), and others. The absence of evi- 
dences of compression and squeezing as also the fact that the sutures 
are often more or less oblique to the planes of sedimentation or may 
form a network of intersecting lines are adverse to this theory. 
The most satisfactory explanation of these remarkable structures 
is the solution theory first proposed by Fuchs (1894) and ably sup- 
ported by Reis (1901, 1902) and Wagner (1913). According to this 
theory the structures are due to unequal solution along planes of 
fracture, or extremely thin partings after the consolidation of the 
rock. As the result of compression due to the weight of the over- 
lying mass, solution will take place more rapidly on the concave 
surfaces opposite the columns, thus causing these to penetrate 
deeper and deeper into opposing surface. The residual clay comes 
to rest as a cap on the top of the column, thus protecting it from 
solution. Fossil shells sometimes found on top of the column favor 
the process, as they are less readily soluble than the inclosing rock. 
