430 PROFESSOR HEDDLE ON 
Certain specimens show slabs of the rock vg nace coated with a thin layer 
of the glossy limonite. 
The rock has a very vitrified appearance ; and the absence of the iron com- 
pound from part of its surface, considered along with the reniform margin of: 
of the portions of limonite which sheathe it, is of difficult explanation under 
any supposition of its having been deposited from water. 
Over the smooth and glossy surface of this limonite, and occasionally also 
over the sandstone itself, there are sprinkled vermiform aggregates of minute 
spheres of coalescent psilomelane. 
The limonite layer is here about the sixteenth of an inch in thickness. 
In other specimens it is about the fourth of an inch, and the surface, though 
glossy, is stalactitically fibrous and rough; globules larger than swan-shot are 
singly or confluently sprinkled over this. 
In still others, the glossy limonite (which sheaths botryoidal psilomelane) 
has a thickness not much exceeding that of a coat of varnish; and upon this, 
large rounded masses lie; and narrow, tortuous, and more recently formed 
drops overlie both the limonite and these drops of psilomelane. 
Of these specimens it may be argued that they are not cases of droppings 
at all, but merely of local segregations of matter which had not deposited itself 
in a uniform layer over the surface of the limonite; and that it had not done 
so on account of the smoothness of the latter not only affording but few points 
or centres for radiant growth, but on account of its oil-like surface acting 
repellantly to the exercise of ordinary adhesion ; and that once that crystalline 
shoots emanated from the few rough centres which did exist, the succeeding 
growths were localised at these,—as is so frequently seen in zeolites of a radi- 
ating character. 
While giving all due weight to this argument, it has to be replied that the 
manner in which the limonite ordinarily coats the psilomelane, negatives the 
idea that there had been any repulsion between the two minerals ; and that the 
above argument in no way meets the fact of some of the drops reposing upon 
the comparatively rough sandstone. 
Certain rare specimens show an apparent flow of molten matter over the 
limonite. 
Others seem occasionally to point to a large drop or drops of a plastic sub- 
stance which has taken a cast of the narrow crevice into which they had fallen. 
None such were found adherent to the wpper part of any drusic cavity. 
The drops have often fitted themselves in between the two coats of the 
psilomelane which had sheathed the surfaces of the rock-rents. 
The specimens which fall to be considered under the fourth head, however, 
seem to be inexplicable upon any view save that of a succession of molten 
masses alighting upon one another, after the lapse of definite periods of time, 
EE 
