SOILS AND FERTILIZERS. 393 



interior. Originally the whole mass was fluid, but the surface has 

 cooled more rapidly than the interior, and so a firm crust has been 

 formed. As the central mass cooled, it contracted, and the crust 

 became wrinkled and folded, as does the skin of an apple as its pulp 

 dries, and, by this folding, great ridges were thrown up in some places 

 and vast depressions formed in others. When the crust became cool 

 enough for water to remain on it, most of the depressions were filled 

 by it, and the " dry land appeared," not only on the crests of the 

 ridges, but on the elevated plateaus about them, and thus oceans and 

 continents were formed. 



Had one of us seen the earth at that time he would have been 

 loath to select it as a residence. Rugged, rocky ranges of precipitous 

 mountains surrounded by stretches of naked rock made the land- 

 scape. Dense clouds from the tepid oceans dashed against the icy 

 peaks, and torrents of water rushed back to the sea. Where the 

 slopes permitted, the glaciers spread over wide areas, for no vegeta- 

 tion checked the rapid radiation of heat, and night brought bitter 

 cold. The crust waved and fluctuated over the liquid interior as 

 does thin ice under a daring skater, and as it fell the sea rushed 

 over the land, only to flow elsewhere as the depressed area rose again. 

 The freezing and thawing and the effects of wind and water in time 

 produced a change. The rocks were riven and broken to powder, 

 their nearly vertical slopes became less steep, and instead of bare 

 rock the earth showed dreary morasses and stretches of sand. 



Over these marshes vegetation began to thrive. In the sea there 

 lived then, as now, a teeming population, animal, vegetable, and 

 living beings that can with difficulty be assigned to either of these 

 classes. Each of them, however, contained carbon, and many had 

 built lime, phosphorus, nitrogen, and other valuable substances into 

 their bodies. Where food was abundant these grew in vast numbers, 

 and though many are infinitely small singly, their aggregate mass 

 is enormous. Among the tiny organisms is one called the Globi- 

 gerina, a being so small as to require a microscope to study it, but in 

 the past, as now, growing in great numbers in the sea. The animal 

 is soft and jellylike, but it forms an outside skeleton of shell of car- 

 bonate of calcium or chalk, a structure that protects it living, but 

 entombs it dead. When death comes, the little Globigerina sinks to 

 the bottom, and its tiny shell helps to cover the sea floor. 



In the days of long ago these lived as now, and when some con- 

 vulsion of Nature lifted the bottom of prehistoric seas, the Globi- 

 gerina ooze was lifted as well, and thus the " limestone " formed. 

 In our land a bed of this kind extends from Alabama to Newfound- 

 land; thence, as the "telegraphic plateau," it passes under the At- 

 lantic, rising into the chalk downs and cliffs of England; then, again 



