Subsurface Laboratory Methods 



163 



LINEATIONS 

 (Includes flow lines, alinement 

 of minerals, inclusions, streakings, etc.) 



These can also 

 be used for 

 special type's of 

 lineation such as 

 intersection of 

 planes, wrinklings, 

 etc., but such uses 

 should be so stated 

 in the Explanation. 



Bearing and plunge of lineation 

 ■-/to 



30* 



Strike and dip of foliation 

 and plunge of lineation 



Vertical lineation 



Horizontal lineation 



JOINTS 



Point of observation 

 is at base of arrow. 



Plunge measured in the 

 vertical plane. If the 

 lineation is measured in 

 the plane of the foliation 

 it is suggested that the 

 term rake be used and 

 that the symbol be shown 

 thus: ^ 



It is recommended that 

 the term pitch be aban- 

 doned as it has been so 

 widely used in both senses 

 and appears on many pub- 

 lished maps indicating 

 the vertical angle. 



Strike and dip of joints 



Strike of vertical joints 



-f 



Horizontal joints 



* On the previous list of survey map symbols, the term "pitch" was applied to 

 lineations measured in the vertical plane. However, many comments have been 

 received urging that the term "plunge" be used instead, as "plunge" was originally 

 defined by Lindgren in this sense and is so defined in the text books of Lindgren 

 and Billings. It was also pointed out that "plunge" has rarely been used in any other 

 sense, and that an increasing number of geologists are adopting Lindgren's definition. 

 For these reasons, the Map Symbol Committee decided to adopt the term "plunge" 

 for the angle measured in the vertical plane. This is the measurement that is usually 

 recorded on geologic maps, but for special structural problems, some geologists prefer 

 to record the angle measured in the plane of the foliation, fault or vein, or in the axial 

 plane of the fold. Lindgren and Billings used "pitch" for this angle. However, "pitch" 

 has been so widely used in both senses and has appeared on so many published maps 

 indicating the vertical angle, that its continued use is likely to lead to further con- 

 fusion. Therefore, after wide discussion with structural geologists, the committee 

 decided to abandon the term "pitch" and to suggest the use of the term "rake" for 

 the angle measured in the plane of the structure. This term has been occasionally 

 used to describe the inclination of ore bodies, but it has never been clearly defined. 



