The Plan of the Earth and its Causes. — Gregory. 105 
in which case the whole world was covered by a universal 
ocean ; but before the dawn of geological history, this ar- 
rangement had been disturbed by the formation of irregular- 
ities in the surface of the lithosphere. Dry land appeared at 
the areas of elevation, and the waters gathered together into 
the intervening depressions. 
The problem, then, of the distribution of land and water 
on the globe is the problem of the distribution of irregularities 
in the surface of the lithosphere. We are accordingly at once 
brought face to face with the question, When were the existing 
irregularities made? If, as many authorities say, these de- 
pressions date from the earliest days of the Earth's history, 
and have lasted unchanged in position throughout geological 
time, then we are thrown back upon some cause which acted 
when the Earth was in its infancy. In that case the question 
is astronomical and physical, instead of geological and geo- 
graphical. 
PRE-GEOLOGICAL GEOGRArHY. 
There have been several attempts to solve the question as- 
tronomically, of which the most important is that of Prof. G. 
H. Darwin. According to his luminous theory, the tidal action 
of the sun on the viscous earth formed two protuberances at 
opposite points of the equator ; one of the protuberances broke 
away and solidified as the moon, which revolved around the 
earth much nearer than at present. As a new equatorial 
protuberance formed the moon pulled it backward, thus caus- 
ing a series of wrinkles in the earths' crust, which persist as 
the main structural lines of the continents. These wrinkles 
ran at first north and south from the equator. But owing to 
the moon's strong pull on the equatorial girdle, this part of 
the earth would tend to revolve more slowly than the polar 
regions. Hence the primitive wrinkles were deformed ; in- 
stead of l>eing meridional in direction, they would trend north- 
easterly in the northern hemisphere, and southeasterly in the 
southern hemisphere. Prof. Darwin points out that some of 
the most striking geographical lines on the earth run in ac- 
cordance with this plan. He instances the eastern coast of 
North jVmerica, the western coast of Europe, part of the coast 
of China, and the southern part of South America. But, with 
