4 BRYOZOAN FAUNA. OF THE ROCHESTER SHALE. 
and the surface characters of the fossils are not so well preserved. However, this is com- 
pensated for by the excellent preservation of their internal features. A considerable fauna 
was determined from the extensive collections made by Mr. Pettit at Grimsby, Ontario. 
COLLECTING IN THE ROCHESTER SHALE. 
The Rochester shale affords ideal localities for collecting by the process of washing. 
The shale immediately above or below the fossiliferous limestone bands almost invariably 
on washing yields free specimens of the species found upon the slabs. Still better results 
are obtained if the fossiliferous limestone layer be traced until it changes into a marl or clay, 
as often happens, for here the fossils ordinarily helping to make up the limestone are more 
complete, and being uncemented can be washed out free. Careful selection of clay from such 
marly pockets or from above or below unusually rich limestone layers will yield excellent 
fossils and save time in the picking out of the specimens after the material has been washed. 
In washing fossiliferous shale the writer has found that the best meihod to obtain the 
specimens in as perfect condition as possible is first to spread out the materia 1 _uid expose 
it to the sun for a day or more. When the clays have been weathered in the field, this, of 
course, is unnecessary. Such an exposure slakes the clay, allows the specimens to dry, and 
thus become less liable to break, and, moreover, causes the clay to disintegrate more readily] 
Then if the marl or clay be allowed to soak for a day, the final washing is a short and simple 
matter, consisting merely in allowing clear water to run over the material until the water i 
passes through without becoming discolored. After the residue has dried, sifting the 
material into several grades of fineness will aid in assorting the specimens. This method 
of washing has the advantage of reducing the breaking of the specimens to a minimum, for 
in the ordinary process the shaking required to hasten the disintegration of the clay breaks 
or otherwise injures the more delicate fossils. 
After washing a sample of fossiliferous Rochester shale it will be found to consist almost 
entirely of fossil remains. The coarse material is composed hugely of fragmentary or entire 
specimens of brachiopods, crinoidal remains, and ramose or massive bryozoa. In searching 
for bryozoa, the fragmentary brachiopods and crinoidal remains should be carefully exam- 
ined, for they are often incrusted by delicate, parasitic species, especially of the Ctenosto- 
mata. In washings from certain localities near Lockport, one out of every three or four 
fragments of Spirifer niagarensis was incrusted by the unique bryozoan Khopalonaria 
attenuata. The finer material usually shows an abundance of the small ramose and fenes- 
trated bryozoa and of young specimens of brachiopods, while the finest siftings afford 
ostracods and other microscopic organisms. 
In England the strata corresponding to the Rochester have been thoroughly searched foi 
fossils by washing, and a large and interesting fauna is the. result. Unfortunately little hat 
been published concerning the bryozoa obtained from these washings, but the numerous 
ostracods described by Jones and I loll and the brachiopods described by Davidson show the 
value of this method of collecting. Mr. Maw's washings are well known to every student 
of the Wenlock. Over 20 tons of these shales were washed by him for fossils. The numbei 
of specimens picked out ran into the thousands for some of the species. The Rocheste 
shale compares quite as favorably in this respect, since from the residue of 50 pounds o 
shale so treated the writer picked out over 5,000 specimens of the bryozoan ChUotrypt 
ostiolata, while other small ramose species, such as Acanthoclema asperum and Bato$tornell< 
granulifera would be found to occur in the same abundance if one should take the troubl 
to assort all of the specimens. If 20 tons of this shale were washed, the specimens of a \ 
least some of these species would have to be recorded by quantity rather than by number I 
Sometimes the fossils of the Rochester are confined entirely to the limy layers. In tlii i 
case if free specimens are desired many of them may be detached from the slabs withou 
injury by means of caustic potash. Entire zoaria, or even average specimens of such fragil ' 
forms as the Phylloporiniche or Fenestellidae, can be had only on slabs of limestone 1 or shale 
The washings will yield small, clean fragments of these for study, but no large, show, 
examples for exhibition. 
