S?4 THE WORLD, 



X 



spire of the church could be seen. In the course of a century it 

 is said that a thousand acres of land in Suffolk were covered by 

 blown sand; and a considerable tract of land on the north coast of 

 Cornwall has been thus inundated, and ancient buildings are of- 

 ten brought to light by its shifting; and in some cases, in boring 

 for water, distinct strata of the sand separated by a vegetable 

 crust are found. The name o dunes, or downs, has been given 

 to these moving sand hills, which are first generated on the sea 

 shore. The sea-breeze drives the fine sand, farther and farther 

 inward, until it accumulates and becomes a formidable hill. 

 There are many instances of these hills in the United States, 

 particularly in the south eastern part of Massachusetts, and near 

 Cape Cod, where they are sixty or seventy feet high, and of al- 

 most snowy whiteness. Here these dunes are moving gradually 

 westward, the strength of the land-breeze not being sufficient to 

 counteract the effect of the sea-breeze. A series of these dunes 

 now threaten the village and Bay of Provincetown, and large 

 quantities of beach-grass have been transplanted to their ridges 

 for the purpose of arresting their progress. 



The chemical agency of the atmosphere is another important 

 means of change producing a sure and often rapid decay of the 

 solid materials of our globe. The forces of chemical affinity are 

 superior to those of cohesion 'and aggregation, and the atmos- 

 phere charged with moisture and carbonic acid gas, disintegrates 

 the solid materials, which crumble away before this "gnawing 

 tooth of time." The resistance which rocks afford to decom- 

 position depends greatly upon their composition, but all are more 

 or less affected. A very slight examination of the soil in any 

 rocky country will suffice (o show that it has been derived from 

 the decomposition of the rocks in the vicinity. In granitic coun- 

 tries we find the soil made up of shining particles of silex or 

 quartz, and spangles of mica, and particles of felspar, and even 

 the finest portions will be found thus composed. Sienite and 

 hornblend rock, when decomposed, yield a darker soil, containing 

 much more felspar and less quartz, while slaty rocks give a dark 

 colored tint to the soil, forming beds of tough blue clay, when 

 deposited by water. We have already alluded to the consolida- 



