BULLETIN 39, UNITED STATES NATIONAL MUSEUM. 



[4] 



The second hammer (fig. 2), designed for trimming purposes, should 

 weigh about three-fourths of a pound, with head not above 3 J to 4 inches 

 in length and faces three-fourths of an inch square, both faces being alike. 

 The handle must be correspondingly more slender and an inch or so 

 shorter. Handles should be of best hickory, and considerably reduced 

 midway between the head and the portion grasped by the hand in order 

 to impart the desired spring to the blow. 



"When transportation facilities allow, it is well to have also a 6-pound 

 sledge, as not infrequently the natural weathered forms of rock masses 

 are such as to necessitate the breaking of sjialls of considerable size 

 in order to obtain material of the desired freshness. Chisels are rarely 



of use. Occasionally what is 

 known among stonecutters 

 as a pitching tool becomes of 

 use in breaking off spalls 

 from the larger blocks (see 

 figs. 3 and 4). 



SELECTION OF MATERIAL. 



Always take the specimen 

 from the i)arent ledge unless 

 absolutely sure that smaller 

 and more accessible masses 

 were derived therefrom. It 

 not infrequently happens 

 that angular blocks fallen 

 from the face of a cliff offer the 

 only satisfactory collecting 

 grounds. Providing there 

 is no glacial or other form of 

 drift in the vicinity such can be utilized with safet5^ Never collect 

 materials the source of which is not known unless designed for the pur- 

 pose of studying drift materials or because the specimen presents 

 itself some points of more than ordinary interest. Few objects are of 

 less value than rock specimens the exact source of which is not known. 

 Collect always fresh material. Many of the collections made by the 

 earlier surveys have been found quite worthless for modern microscopic 

 work, owing to the fact that they were so altered by weathering. The 

 outside weathered surface should always be first broken away until a 

 bright fresh fracture is shown. In some compact, close-grained rocks 

 weathering proceeds so uniformly as to form on the outer surface 

 only a thin crust of oxidation products, so that a single specimen will 

 serve to show both weathered and fresh material. As a rule, however, 

 it will be found best, in case weathered material is also desired, to col- 

 lect these in separate specimens. Take particular care to secure repre- 

 sentative specimens. If any apparently essential variation is shown 

 in the niass of the rock, collect typical materials from each and label 

 so as to show their relations — which is the prevailing type, etc. 



Pig. 5. — Manner of holding specimen. 



