8i8 NORTH AMERICAN INDEX FOSSILS. 



nearly as possible to the horizontal elements. Similar care must 

 be exercised in making sections of Bryozoa. Here the longitudinal 

 sections should expose the whole length of the zooids if possible. 

 Frequent examination during the first grinding will therefore be 

 necessary. 



Sections of cup corals require the use of a saw. An ordinary 

 band saw with steel holder will serve for calcareous specimens, 

 when used with water, or water and emery. In this case a guide 

 should be arranged so that the cutting produces a smooth surface. 

 A rapidly revolving tin disc with water dripping over it and fine 

 emery gives better result — while the best are obtained when the 

 disk is trimmed with diamond bort. After the first sawing of the 

 coral, the two surfaces resulting should be ground smooth and 

 finished with pumice powder, and then cemented to a glass plate, 

 before the second sawing. Do not saw the sections too thin — 

 leave much to subsequent grinding. Often the polishing of the 

 sawed surfaces is sufficient to show the internal structure. 



The same method is employed in making sections of cephalopods. 

 When it is necessary to get at the younger stages of ammonoids, 

 the older whorls must generally be broken off; this should always 

 be done under water. 

 6. Coating of Fossils to Bring out Detail and for Photographing. 



Impressions of fossils often show the detail in much greater clear- 

 ness if they are covered with a coating of impalpable white powder. 

 Ammonium chloride powder has been found very satisfactory. 

 Various kinds of apparatus have been used for this purpose. ^^ 

 A simple method devised by Mr. J. E. Hyde of the palseontological 

 staff at Columbia University, is as follows : Two 8-ounce wide 

 mouth wash bottles, each about half full, the one of ammonia, the 

 other of hydrochloric acid are connected with a third, which is 

 about half full of water, by bent glass tubes through rubber corks. 

 These tubes extend to near the bottom of the acid and ammonia 

 bottles, their ends being submerged in the liquid, but in the water 

 bottle they end just below the cork. The mouth piece from the 

 last wash bottle extends to near the bottom of the bottle, being sub- 

 merged in the water. The water also serves to absorb the gases 



"See Van Ingen, New York Academy of Science, Annals, Vol. 14, P- 115-116, 

 1902. 



