Monthly Microscopical | PROGRESS OF MICROSCOPIOAL SCIENCE. 165 
stone is plainly laminated, and has clearly been thrown down beneath 
water, it being readily cleavable into more or less distinctly marked 
laminw. Almost universally the flexibility is attributed to the presence 
of mica, but the brighter-coloured specimens which I have examined 
contain no mica, and yet possess the property of being readily bent 
to a very marked degree. Even in the red-tinted specimens there 
are large portions in which no mica is found. Dr. Wetherill says, 
that by examining the Itacolumnite by means of the microscope he has 
been enabled to ascertain that the “flexibility is due to small and 
innumerable ball-and-socket joints which exist throughout the mass of 
the stone very uniformly. Each joint permits a slight movement 
which is always greater in one direction.” Now I must say that, 
though I have come to the investigation prepared with considerable 
faith, yet, after many careful examinations, I was never able to force 
my imagination to the extent of getting it to show me anything 
resembling ball-and-socket joints. The examination need not always 
be made of the opaque sandstone, but portions can be roughly crushed 
and mounted in Canada balsam so that light may be transmitted 
through them and the mode of their interlocking plainly made 
evident. The fact is that the rock is made up of small, broken, 
irregular masses of transparent sand which evidently have not been 
carried any great distance by water, as their sharp edges have not 
been at all abraded, but, on the contrary, remain, but they have 
evidently been broken off from a rock which had a conchoidal fracture, 
they being little plates of extremely irregular outline. Thus, when 
they settled in the liquid in which we can suppose them to be thrown 
down, they naturally, for the most part, distributed themselves with 
their greatest axes in the same direction, and hence the lamination 
and cleavage of the rock itself. We can readily understand that in 
such a rock, if the particles were not strongly held together, that 
they would possess a certain amount of motion one over the other, 
and this motion would be most marked in a direction at right angles 
to the lamination, which is the case. But, also, such a rock would 
not be elastic, only flexible, and gradually, after several times bending, 
be broken. Such is exactly the case with Itacolumnite. In fact any 
one possessing a microscope and a fragment of this rock, can readily 
verify my observations and demonstrate that Dr. Wetherill’s proposed 
name of Articulite is inappropriate for Itacolumnite. In conclusion, 
I would mention that grains of the crushed rock when put up in 
Canada balsam become very beautiful objects for examination by 
means of the micro-polariscope, exhibiting a gorgeous display of 
colours when the interposing selenite film is used. 
The Structure of Graptolites—Myr. John Hopkinson, in an article 
published in the ‘ Geological Magazine, says that the name Dicra- 
nograptus was proposed by Hall, in his ‘Memoir on the Graptolites 
of the Quebec Group,’* for certain forms of Graptolites, some of which 
were then included in the genus Didymograpsus, and others in Diplo- 
grapsus. He, however, only considered these forms as constituting a 
sub-generic group of his genus Climacograptus, believing them to have 
be dee Ale 
