398 Original Articles. [July, 
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Fie. 3. 
Fig. 3. Is the section of a Lunar Crater, showing how by the 
eruption, and subsequent deposition of the ejected matter, the circular 
outer wall or crater had been formed. 
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Fie. 4. 
Fig. 4. The section of the same, exhibiting the manner in which the 
central cone had resulted from the expiring efforts of the eruptive action. 
Tn examining the Moon’s surface, we cannot but be impressed with 
the vast dimensions of many of the volcanic craters with which her 
surface is studded. Craters of thirty miles: and upwards in diameter 
are by no means uncommon, and the first impression on the mind in 
reference to such magnitudes is one of astonishment, that so small a 
planet as the Moon (whose magnitude is only about jth that of the 
earth) should exhibit evidence of volcanic violence so far greater than 
any that we have on the earth. This apparent paradox will, however, 
disappear when we come to consider that in consequence of the Moon 
being so much less than the carth, the force of gravity on its ex- 
terior is not above 4th of that on the earth, and that the weight of 
