172 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



with which they have had experience. Moreover, the geologist gees 

 what he has been trained to see and overlooks much that he would 

 otherwise see had he the necessary background of experience. In 

 study of the surface features of the moon he is confronted with con- 

 ditions with which he has had no contact. Lunar surface feature? 

 have been sculptured by catastrophic agents of different kinds and 

 not by the action of running water, or by erosion and deposition in 

 the usual sense, or by ordinary wind action, or by weathering. Grav- 

 ity is only one-sixth of that on the earth; a mas? of rock weighing 

 a ton on the earth would weigh only 333 pounds on the moon. At 

 the moon's surface there is no water, no ice ; no protective blanket of 

 atmosphere to soften the impact of the sun's rays and to prevent the 

 escape of heat radiated from the moon's surface. The temperature 

 ranges are extreme. At midday on the moon, with the sun directly 

 overhead, the surface temperature is approximately 120° C. (250° F.) 

 or above that of boiling water; at midnight it falls to below 

 — 100° C. ( — 150° F.). In spite of this extreme range in surface 

 temperatures it is probable that a few feet below the lunar surface 

 the inflow of sun's radiation maintains a temperature not far from 

 freezing, or 0° C. 



It is not an easy task for the geologist to adjust his mental attitude 

 to such extreme conditions. He has become accustomed, on viewing 

 a given terrestrial surface feature, to inquire (a) of what kinds of 

 rocks or materials does it consist; (&) what geological agents, oper- 

 ating on the original rock mass, have given the surface feature its 

 present shape? He has learned to recognize the imprint or earmark 

 of each kind of geological agent and seeks in a given case to ascer- 

 tain what combination of geological agents or processes, acting one 

 after the other or together, have produced the surface feature under 

 study. By this method he is able to read and to interpret geological 

 history as it is written in the rocks and on their siirface. In his 

 study of the surface features of the moon he is confronted with 

 physiographic forms which, in part, are quite unlike anything he has 

 seen on the earth ; also, he misses the familiar effects of erosion. To 

 him the surface of the moon presents a weird picture. He realizes 

 that before he can begin to make progress on lunar physiographic 

 problems, he must first ascertain the nature of the materials which 

 he sees exposed on the moon; then determine how those materials 

 behave under the known lunar surface conditions. In other words, 

 he must acquire a good working knowledge of the petrology of the 

 lunar surface materials. In addition, he needs a good lunar map, 

 preferably a topographic map, by use of which he can obtain an 

 idea of the spatial relations of the different features. This is asking 

 a good deal and the task might seem hopeless were it not for the 



