8o6 NORTH AMERICAN INDEX FOSSILS. 



Concretions often yield good fossils, but are hard to break. 

 Building a fire around a concretion or other resistant rock and 

 heating it, often makes it quite brittle. Water may be poured over 

 the mass, when highly heated, or the smaller nodules may, after 

 heating, be dropped into water. Pyrite concretions from fossi- 

 liferous shales are best treated in the laboratory. 



Unconsolidated clays and marls seldom yield their fossils un- 

 broken. It is best to cut them out with enough clay adhering to 

 keep the mass intact, leaving the final preparation for the labora- 

 tory. Stanton suggests covering the pieces before packing with a 

 coat of common hot furniture glue to prevent cracking and crumb- 

 ling in drying. Such marls should always be packed in small boxes. 

 Sands and clays rich in small fossils are best shipped in bulk to the 

 laboratory where the sorting is more practicable. Of course, if 

 necessary, the laboratory method may be employed in the field so 

 far as apparatus is available. Clays resulting from weathering 

 of fossiliferous shales should be collected in bulk, as they contain 

 many good small specimens. 



In general the collector should bear in mind that good collections 

 can be made only with care. On weathered surfaces it is well to 

 get down on hands and knees and carefully pick over the ground, 

 taking everything in sight. Do not stop to examine your material 

 too closely, and do not throw away a specimen because you think 

 it is a duplicate. Extensive collecting alone will save the rarer 

 species, and a large series of even the common forms is desirable, 

 for it shows the variation of the species. Discarding of specimens 

 is best done in the laboratory, where they can be carefully studied. 

 Hasty collecting, unless absolutely necessary, should be avoided — 

 it takes time to get the material of a good collection together. 

 Furthermore, it is a great mistake to pass by a good locality, or 

 even a moderately good one, because it is inconveniently situated 

 and in the hope of finding a more convenient one elsewhere. Such 

 hope is often doomed to disappointment. 



The collector should always take the greatest care to determine 

 and record the exact position of his fossil in the section studied. 

 The field notes should always be accompanied by a sketch (prefer- 

 ably in colors) of the section, the beds numbered or lettered, and 

 the collections labeled accordingly. 



