26 THE PALEONTOLOGY OF MINNESOTA. 
{Preparation of shale and chalk. 
balsam will be hard when cold. As these “trial slides” are seldom of any value, 
it is not necessary to use cover glasses if the balsam is hardened, as above directed. A 
careful examination of these slides under the microscope with a good 4or 4 inch 
objective will decide as to the value of the material under observation, and if it 
proves to be only sand, pour it all out, wash the bottle, and again try the same 
process with another sample of clay. But if the slides show a few good fossils, the 
next step is to separate them as much as possible from the mass of sand, ete., with 
which they are associated. In this as in the first washing, specific gravity will do 
most of the work. Pour off most of the water and put the shells, sand, ete., into a 
4 oz. beaker (or glass tumbler), wash out the bottle, fill the beaker about $ full of 
water, and after it has rested ten minutes, pour ? off the top through a glass funnel 
into the bottle, repeating this 5 or 6:times. As in the first washing, mount and 
examine a few slides from the material at the bottom of the bottle, mounting and 
preserving slides, if found to be of value. If nothing of value is found, pour out the 
contents of the bottle, and fill up again as before from the beaker, after five minutes 
rest repeating these washings and examinations at shorter resting intervals of say 
three, two, and one minute, or less, until nothing but the coarsest sand remains in 
the beaker. In that there may be a few good specimens of Polycystina. Hach layer 
of the clay, as deposited by its specific gravity, has now been examined, and most of 
the fossils are contained in some one or possibly two of them. Nineteen-twentieths 
of the original sample of clay have been washed away, and in the selected one-twen- 
tieth that remains there may be one fair fossil to one hundred grains of sand. 
Shale. The fossil contents of most of the softer shales can be secured by breaking 
up the specimen with a pair of strong pliers, crushing the shale while under water 
and edgewise of its lamine. This will free many of the fossils without breaking 
them ; then boil the firmer parts of it for a few minutes (or longer if the material 
requires) in a rather strong solution of washing soda, and wash and separate the 
fossils from the fine shale, sand, ete., by repeated decantations, as directed in the 
treatment of clay. 
Chalk. Foraminifera, coccoliths, rhabdoliths, with an occasional radiolarian 
(Polycystina), of which the “farmer’s chalk”, or soft limestone, is largely composed, 
can be freed from the rock by washing off the surface of a clean piece of it with a 
rather stiff brush while under the surface of the water in a bowl or basin. The 
water will soon become as white as milk. The specific gravity of the Foraminifera 
and Radiolaria will promptly carry them to the bottom, and they can partly be sep- 
arated from the sand, etc., by repeated washings, decantations, etc., as directed in 
the treatment of clay ; but unless great care be taken in this washing, the coccoliths 
