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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



oldest, containing earth's first preserved creation, all, with the exception 

 of Lingula and Nautilus, which persist to the present day, extinct species, 

 often very unlike those now existing, but, we believe, well adapted to their 

 environment. The Secondary strata contain no animal remains which 

 can be identified with existing species ; those which are found in them 

 are nearly all different from those which occur either in the Tertiary 

 above or the Primary strata below. The Tertiary strata are characterized 

 by containing, among other fossils, the remains of animals which are 

 identical with existing species. England has been called " the Paradise 

 of the geologist," because, coming from the oldest rocks in the West to 

 the youngest in the East, it contains examples of nearly all the beds of 

 rock which exist in any part of the world. 



Stratified rocks consist of repeated alternations of limestone, sand- 

 stone, and clay, or mixtures of two or more of these earthy substances. 

 The mixing largely modifies the character and often improves the 

 fertility ; thus chalk mixed with clay produces a better soil than either 

 the chalk or the clay unmixed, as the one supplies what the other lacks. 

 Again, where a sandstone meets a limestone, the sandy soil is benefited 



Fig. 74. — Diagram showing influence of incline on Fertility. 

 (From "Agricultural Geology," by Primrose McConnell, B.Sc.) 



by the addition of lime. The same happens when clay or marl is added 

 to sandy soil ; both the sand and the clay are improved by mixing. 

 Owing in some places to glaciers and icebergs in bygone ages, rocks, 

 gravel, sand and clay have been transported from their original home and 

 carried and deposited elsewhere. Where this drift or transported matter 

 is deposited, it alters the character of the soil from that in the neighbour- 

 hood lying over the same strata, as the soil is more dependent on the 

 character of this transported material on the surface than on that of the 

 rock below. The height above the sea, the mean temperature, the quantity 

 of rainfall, whether hilly or flat (fig. 74), and even aspect, all somewhat 

 modify the soil and its fertility, even when overlying the same rock ; 

 nevertheless, allowing for the modification, the same rock produces a 

 similar class of soil all the world over. 



Igneous Bocks.— Starting with the igneous or fire-formed rocks, we 

 will first consider granite, of which the characteristic minerals are quartz 

 and felspar, with mica in lesser proportion. These, when decomposed, 

 yield sand, alumina, and potash. The quality of the soil is dependent 

 largely on position. Where mountainous or forming steep hills, as is 

 the case in most of the granite districts in Cornwall and Devonshire, it is 



