MANUAL FOR NONCOMMISSIONED OFFICERS. 819 



Now flood your lake deeply enough to cover up the features 

 yon have introduced. The new water line, about as shown by 

 the dotted line in figure 11, shows the oblong shape of the 

 depression at a higher level ; the solid lines show the shape 

 farther down ; the horizontal distance between the two con- 

 Put together the information each of these contours gives you, 

 and you will see how contours show the shape of the ground. 

 On the little map you have drawn you have introduced all the 

 varieties of ground forms there are ; therefore all contour forms. 



The contours on an ordinary map seem much more compli- 

 cated, but this is due only to the number of them, their length, 

 and many turns before they finally close on themselves. Or 

 they may close off the paper. But trace each one out, and it 

 will resolve itself into one of the forms shown in figure 11. 



Just as the high-tide line around the continents of North 

 and South America runs a long and tortuous course, but finally 

 closes back on itself, so will every contour do likewise. And 

 just as truly as every bend in that high-tide mark turns out 

 around a promontory, or in around a bay, so will every bend 

 in a contour stand for a hill or a valley, pointing to the low- 

 lands if it be a hill, and to the height if it mark a valley. 



If the map embrace a whole continent or an island, all the 

 contours will be of closed form, as in figure 11, but if it em- 

 brace only a part of the continent or island, some of the con- 

 tours will be chopped off at the edge of the map, iind we have 

 the open form of contours, as we w^ould have if figure 11 were 

 cut into two parts. 



The closed form may indicate a hill or a basin ; the open 

 form, a ridge or a valley ; sometimes a casual glance does not 

 indicate which. 



Take up, first, the contour of the open type. If the map 

 shows a stream running down the inside of the contour, there 

 is no difficulty in saying at once that the ground feature is a 

 valley; for instance, V, V, V, and the valley of Corral Creek 

 on the map. But if there is no stream line, does the contour 

 bend show a valley or a ridge? 



First of all, there is a radical difference between the bend 

 of a contour round the head of a valley and its bend round 

 the nose of a ridge. 



