THE GENESEE FARMHIl. 



IDEAL SECTION OF THE EARTH'S CRUST. 



^gricttltnral <^ealogti. 



The well-informed farmer should have some knowl- 

 edge of the science of Geology. Without it, he can 

 have no correct ideas as to the origin and peculiari- 

 ties of soils in different localities ; and of their natu- 

 ral adaptation to certain crops, and lack of adapta- 

 tion to others. In connection with this article, the 

 reader will see an ideal section of the earth's crust, 

 from its surface down to the region whence melted 

 minerals are forced up by a mechanical power, too 

 large for circulation. 



Rocks are best studied under two general heads : 

 First, Those that were melted by heat, and cooled to 

 attain the form in which we see them. These are 

 denominated Igneous Rocks, from the Latin word ig- 

 nis, u fire," because fire was an active agent in 

 bringing the matter that forms such rocks into the 

 peculiar conditions in which they appear. Second, 

 Those that were deposited like sediments in water, 

 compressed and consolidated by great weight into 

 hard masses. Such are called Aqueous rocks from 

 aqua, " water," and also Sedimentary rocks. 



Among the igneous rocks, granite is generally the 

 lowest in the earth, and by far the most abundant. — 

 In the section which we have given granite, will be 

 seen to underlie the several formations denominated 

 Primary, Secondary, Tertiary, Drift, Alluvium and 

 Lava. The latter coming from an active volcano is 

 presumed to run down its cone and cover the highest 

 aqueous deposite, whether it be the alluvium of a 

 river, or other recent deposition from water. It is a 

 singular fact that some of the best soils in the world 

 are formed of the debris of lava, which was devoid of 

 all organic matter, and brought up thousands of feet 

 from Nature's mighty furnace, whose fire burns on 

 from century to century with undiminished intensity. 

 Taking the hint from dame Nature, agricultural 

 chemists have burnt granite till it would crumble in- 

 to powder when treated with a dash of cold water, 

 and finally give up to growing plants its fertilizing 

 elements. 



Rocks formed by ancient volcanoes are called 

 " T/-</p," as will be seen in the drawing. The word 

 trap ia derived from trappa, which means a stair or 

 step. Greenstone pnd basalt belong to the trap family. 



Melted matter injected into fissures in mountain 

 masse? of granitic and sedimentary rocks appears as 

 veins of granite, serpentine, porphyry, syenite and 

 other minerals. Syenite differs from granite in hav- 

 ing horneblende take the place of mica. The last 

 named mineral is called isinglass in some sections of 

 country. Granite is composed of the three well 

 known minerals, quartz, felspar and mica. Porphyry 

 is distinguished by its large crystals of felspar. — 

 There are several varieties of this famous classic 

 rock. Serpentine contains about 40 per cent of mag- 

 nesia. It is essentially a silicate of that base. — 

 Among the Primary rocks gneiss is the most impor- 

 tant. It is simply stratified granite — the consolida- 

 ted debris (fragments) of the parent unstratified rock. 

 When granite is decomposed, as well as disintegra- 

 ted, sand, shale and slate rocks are produced — the for- 

 mer from quartz and the latter from felspar and mica. 

 Primary lime-stone is also formed from the decomposi- 

 tion of crystaline rocks which contain that mineral. 



Secondary rocks are a numerous family. They 

 are conveniently divided into five systems ; all of 

 which abound in the well preserved remains of ex- 

 tinct races of animals. The lowest in the catalogue 

 is the Silurian system. Above this is the Coal- 

 bearing system ; then the Salt-bearing : Oolitic, and 

 Chalk systems. These, when entire, are several 

 thousand feet in thickness. 



Tertiary strata are divided by Lvell into four 

 groups, to which he gives the names of Eocene, 

 Miocene, Older and JYcwer Pliocene. These terms, 

 derived from the Greek, we will not stop to define. 



Above the tertiary strata lie the Drift, which is the 

 same as the diluvium of some geologists. It is the 

 loose earthy matter above all solid rocks, as it was 

 left at the time when islands and continents were last 

 elevated by volcanic action above the surface of the 

 ocean. So far as rains, snows, creeks, rivers, and 

 lakes, have transported this moveable earthy matter, 

 or the debris of exposed rocks, and deposited it in 

 new layers, since dry land appeared as we now see, 

 these latest deposits or strata are called alluvial beds, 

 or alluvium. Such strata abound in the remains of 

 plants and animals now living on the continent. The 

 alluvial and drift formations are most worthy of the 

 attention of practical farmers. 



