MICROSCOPY. 439 
Bow.pers IN CoaL.—In the May number of the NATURALIST 
(page 291), is an extract from the “ Report of the Ohio Geological 
Survey,” in which Prof. Andrews describes the occurrence of a 
quartzite bowlder in the coal of Ohio. This bowlder, he thinks, 
must have been transported there by ice; and to account for the 
ice he supposes a much colder climate for the coal period than 
most geologists would be willing to admit. It seems to me that a 
much simpler explanation, which dispenses with the supposed cold 
climate, is quite sufficient to account for the facts. It is well 
known that, during freshets, trees on the banks of streams are often 
undermined, and floated away, bearing in their roots large stones, 
which may thus be carried to great distances. In this way the 
small bowlder found in the coal of Ohio might easily have been 
transported. Similar instances of bowlders in seams of coal have 
been observed in this country and in Europe.—O. C. Marsu. 
Foon or Presrosaurvs.—At a meeting of the Academy of Nat- 
ural Sciences, May 28th, Prof. Cope exhibited some vertebrae of a 
Plesiosauroid reptile and those of a smaller species, probably a 
Clidastes which were found in close proximity near Sheridan, 
Kansas, by Joseph Savage of Lawrence. According to this gen- 
tleman the vertebrate column of the Clidastes was found imme- 
diately below that of the Plesiosauroid and in a reversed position, 
as though it had been swallowed by the latter or larger reptile. 
The largest vertebra of the Clidastes were about three-quarters 
the length and one-fourth the diameter of those of the Plesiosau- 
roid, and the animal must have furnished a large or, at least, a long 
mouthful for its captor. The bones of the Clidastes were not in 
good condition, but resembled those of C. cineriarum Cope, 
though smaller. The Plesiosauroid was a species of over thirty 
feet in length and was the third species found in Kansas. It was 
new and was named Plesiosaurus gulo. 
* 
MICROSCOPY. 
A New Erecrine Prism. — Mr. J oseph Zentmayer exhibited, at 
a meeting of the Franklin Institute, a single prism which erects the 
‘mage completely and in such a way that the incident and emerging 
rays are parallel, which, as far as we know, was never accom- 
Plished before. In connection with the microscope, as it was 
shown, it interfered very little with the definition, and, although 
