proceedings: geological society 293 



The temperature differences found by measurements at different 

 levels in the fumaroles of the Valley are, however, on a larger scale 

 than any that are ordinarily observable experimentally, and it is still 

 possible that some other factor may be active in addition to the ve- 

 locity cooling. 



T. W. Vaughn : Note on Eocene corals from Peru and on other fossils 

 from Haiti and Trinidad. 



REGULAR PROGRAM 



F. K. Matthes: Relief shading of topographic maps. The most 

 difficult thing which cartographers and topographers have to deal with 

 is representing the vertical element in the delineation of land features. 

 This delineation can be done in several ways as by hachuring, con- 

 touring, and by shading. Hachuring has been developed to an art in 

 Europe. It requires a draftsman with a steady nerve and hand, and 

 the reproduction of his work by expert engravers. The art had reached 

 fine execution by 1815, yet in Europe, long ago, hachuring was replaced 

 by shading. The same effect is obtained with perhaps one-twentieth 

 the cost. Shading represents land forms perhaps more adequately 

 than hachuring and can be used to better advantage and more generally 

 than hachuring. 



For the last three decades in the United States we have devoted our 

 energy almost exclusively to contouring. No country has done better, 

 but we have used contours where their use was at a disadvantage. 

 Delineation of land forms has been attempted also by hypometric tints 

 but these must be based primarily on contour work. It is a good 

 practice for hachuring and shading to be done as if a relief model were 

 hung vertically on a wall and illuminated above and to the left. In 

 experimental work done by J. H. Renshawe, of the U. S. Geological 

 Survey, this lighting element has been employed but Mr. Renshawe has 

 developed one method different from that of European topographers, 

 in that dark shading is used to express the lowest altitude of river 

 areas, whereas in European maps lowlands are lighter and high plateaus 

 are dark. On shaded maps made recently by the U. S. Geological 

 Survey, high plateaus are given a light shading and flat areas close to 

 sea level are given a deep shading. This obviates confusion found on 

 European maps in which both the mountain tops and the valley bot- 

 toms are given the same high light. 



O. E. Meinzer: Quantitative methods for estimating ground-water 

 supplies. This paper relates only to ground water, or phreatic water — 

 that is, water in the zone of saturation. It is not concerned with the 

 subsurface water that occurs above the water table. It relates not 

 to the quantities of water stored in the earth but to the rate of replen- 

 ishment of the ground-water supply, on which conservation develop- 

 ments must be based. 



Four principal groups of methods are used to determine the annual 

 recharge or the "safe yield" of ground water: the Intake, Discharge, 

 Water-table, and Underflow methods. The first of these consists in 



