ACCOUTREMENT OF A FIELD-GEOLOGIST. yog 



It is of paramount importance that the field-geologist should go 

 to his work as lightly equipped as possible. His accoutrements 

 should be sufficient for their purpose, and eminently portable. You 

 may judge of the portability which may be secured when I tell you 

 that I have on my person at this moment all the instruments necessary 

 for carrying on a geological survey, even in the detailed manner adopt- 

 ed in the Geological Survey of this country. You observe, therefore, 

 that a fully-equipped field-geologist need not betray his occupation 

 by any visible implement. The want of such tokens of his craft 

 often greatly perplexes rustic observers, to whom his movements 

 are a fruitful source of speculation. I shall divest myself of my 

 accoutrements one by one as I have occasion to refer to them, and 

 describe their uses. 



The hammer is the chief instrument of the field-geologist. He 

 ought at first to use it constantly, and seldom trust himself to name 

 a rock until he has broken a fragment from it and compared the fresh 

 with the weathered surface. Most rocks yield so much to the action 

 of the weather as to acquire a decomposed, crumbling crust, by 

 which the true color, texture, and composition of the rock itself, may 

 be entirely concealed. Two rocks, of which the outer crusts are simi- 

 lar, may differ greatly from each other in essential characters. Again, 

 two rocks may assume a very different aspect externally, and yet 

 may show an identity of composition on a freshly-fractured internal 

 surface. The hammer, therefore, is required to detach this outer de- 

 ceptive crust. If heavy enough to do this it is sufficient for your pur- 

 pose ; any additional weight is unnecessary and burdensome. A 

 hammer, of which the head weighs one pound or a few ounces more 

 is quite massive enough for all the ordinary requirements of the 

 field-geologist. When he proceeds to collect specimens he needs a 

 hammer of two or three pounds, or even more, in weight, and a small, 

 light chipping-hammer to trim the specimens and reduce them in bulk 

 without running a too frequent risk of shattering them to pieces. 



Hardly any two geologists agree as to the best shape of hammer; 

 much evidently depending upon the individual style in which each 

 observer wields his tool. This (Fig. 1.) is the form which, after long 

 experience, we have found in the Geological Survey to be on the 

 whole the best. A hammer formed after this pattern combines, as 

 you observe, the uses both of a hammer and a chisel. With the 

 broad, heavy, or square end, you can break off a fragment large 

 enough to show the internal grain of a rock. With the thin, wedge- 

 shaped, or chisel-like end, you can split open shales, sandstones, schists, 

 and other fissile rocks. This cutting or splitting edge should be at 

 a right angle to the axis of the shaft. If placed upright or in the 

 same line with the shaft, much of its efficiency is lost, especially in 

 wedging off plates of shale or other fissile rocks. 



A hammer shaped as I recommend serves at times for other than 



