ACCOUTREMENT OF A FIELD-GEOLOGIST. 713 



an 



Horizontal strata. 



Inclined 



refer here to the use of variously-colored pencils for expressing at once, 

 upon map or note-book, the different rock-masses which may occur in 

 a district. Water-colors are, of coui'se, ultimately employed for rep- 

 resenting the geological formations on the finished map. But a few 

 bits of colored pencils carried in his pocket save the geologist much 

 needless writing in the field. To a red dot or line he attaches a par- 

 ticular meaning, and he places it on his map without further explana- 

 tion than the local peculiarities of the place may require. 



This leads me to remark, also, that he necessarily adopts a system 

 of signs and contractions on his map, not only to save writing, but to 

 prevent the map from being so overcrowded with notes as to become 

 hopelessly confused. Every field-geologist insensibly adopts contrac- 

 tions of his own. For the fundamental facts of geological structure, 

 however, it is eminently desirable that the same signs and symbols 

 should be used with the same meaning on all published geological maps. 

 The subjoined diagram (Fig. 3) shows some of the signs used on the 

 maps of the Geological Survey of Great Britain and Ireland. 



Such are the few prime instruments required in field-geology. We 

 may add others from time to time, according to the nature of the 

 work, which in each region will naturally sug- 

 gest the changes that may be most advanta- 

 geously made. A small bottle of weak hydro- 

 chloric acid, carried in a protecting wooden 

 box, or case, is sometimes of use in testing for 

 carbonates, particularly in regions where rocks 

 of different characters come to resemble each 

 other on their weathered surfaces. When Sir 

 William Logan was carrying on the survey 

 of the Lauren tian limestones of Canada, he re- 

 ceived much help from what he called his "lime- 

 stone spear." This was a sharp-pointed bit of 

 iron fixed to the end of a pole or a walking- 

 stick. He enlisted farmers and others in his 

 operations, instructed them in the use of the 

 spear, and obtained information which gave 

 him a good general notion of the distribution 

 of the limestone. The spear was thrust down 

 through the soil until it struck the rock below. 

 It was then pulled up, and the powder of stone 

 adhering to the iron point was tested with acid. 



If, after trying a number of places all round, the observer uniformly 

 obtained a brisk effervescence when the acid drop fell on the point of 

 his spear, he inferred that the solid limestone existed below, and 

 noted the fact on his map accordingly. 



When the Geological Survey was busy with the great Wealden 

 area of the southeast of England, my colleagues used what they nick- 



Undulating 



Contorted 



-e> 



5 

 9 



Vertical 



Anticlinal axis. 



Synclinal 



Strike of cleavage. 



Direction of gla- 

 cial striae. 



Lead. 



Iron. 



Copper. 



Fig. 3. Some Useful Signs 

 in Geological Surveying. 



