aio OUTLINES OF FIELD-GEOLOGY i XRT n 



It is particularly useful to enter in the note-book 

 sections of the ground just examined, giving what may 

 be at the time the observer's interpretation of the structure 

 of the rocks. Even though these are thrown aside in the 

 end, or superseded by others based on wider experience, 

 they serve their purpose by fixing in the mind what has 

 been seen, and directing attention to the points on which 

 the evidence is defective. A good working hypothesis, 

 so useful in all kinds of scientific work, when employed as 

 a help and not as a master, is specially serviceable in field- 

 geology. One such hypothesis after another may have 

 to be abandoned, but each performs its work in leading 

 the observer nearer to the true solution of his problem. 

 And it is as embodying his working hypothesis of the day 

 that these rough tentative sections in the note-book, 

 made while all the first impressions are still fresh and 

 clear, derive their chief value. 



If the geologist is gifted with any power of sketching 

 he will take care that his pencil drawings or outlines 

 all perhaps that his time and work will allow in the field 

 are secured before getting rubbed, as they are sure to 

 do if carried without precaution in his everyday note- 

 book. They may be fixed in the ordinary way with. 

 gum -water, isinglass, white of egg, or skimmed milk. 

 But I have found it preferable to wash them with sepia, 

 indian-ink, Payne's grey, or some other medium. The 

 pencil-lines are thus fixed, while at the same time, with 

 two or three tints of colour, the sky and relative tones 

 or values of the landscape may be given. If water-colour 

 can be rapidly used in the field this is still better ; but 

 in my own experience the temptation to make a sketch 



