28 OUTLINES OF FIELD-GEOLOGY 



size, uniting the uses of a common notolmok ami a 

 sketch-book, is seven inches long by four and a (juaiter 

 inches broad. Where geological exposures have 

 <arcfully sketched to accurate scale it is desirable to make 

 use of paper ruled into squares. Two sets of lino, 

 expressed either by a watermark in the paper or by 

 coloured ruling, cross each other at right angles and t lie- 

 squares thus produced serve for incln r yards, as 

 the observer may choose. With a foot-rule or tape lim- 

 he measures the proportions of his section, and li 

 difficulty in plotting these accurately on his ruled p; 



Let me remark in passing that perhaps no accomplish 

 ment will be found so useful by the field-geologi 

 power of rapid and effective sketching from nature. If 

 he has this power in any degree, he ought sedulously to 

 cultivate it Even though he may never produce a 

 picture, he can catch and store up in his note-book 

 impressions and outlines which no mere descriptions 

 could recall, and which may be of the highest value in his 

 subsequent field-work. This is true of ordinary detailed 

 surveys, and still more of rapid reconnaissances which 

 may have their ultimate usefulness enormously incn 

 if the observer can seize with his pencil and carry away 

 the forms of surface as well as the geological relations of 

 the region through which his traverse lies. 



Photography may now be advantageously enlisted in 

 the service of field-geology. Cameras are so portable 

 and inexpensive, and the use of gelatine films has made 

 them so light, that the observer may, without greatly 

 burdening himself, add one to his equipment. Even the 

 smallest plates, if sharp in definition, may be of extreme 



