FOR ENGLISH IMMIGRANTS. 7 



heat of the tropics as compared with that of the north polar regions — 

 the upper warmer current constantly flowing to the pole while the lower 

 colder one returned to the equator — tended continually to carry the 

 lighter, finest particles, and the soluble portions of the disintegrating 

 rocks of the north farther and farther south, and to deposit them in beds 

 under the deeper waters of the existing southern ocean. The finer were 

 the particles to a greater distance were they carried by the waters before, 

 by gradual subsidence, they found a resting place as a sediment, which 

 in the course of time was to become a rock. 



Hence geologists inform us that, even in strata which had been 

 deposited or formed at the same geological time, the rock layers at 

 the North are sometimes formed of coarse-grained, insoluble, silicious 

 material, while those farther South and West are limestones, or fine- 

 grained shales, rich in phosphates and other soluble materials. 



Another geological cause of the comparative fertility of Kentucky ■ \ 

 soils is, that these rock strata, out of which they were formed, and which 

 are made up of the most finely divided or soluble materials, were raised 

 above the general surface of the primeval ocean very early in geological 

 history, and have therefore been exposed to the disintegrating influence 

 of the atmospheric agencies for immense unknown ages, so that soils 

 formed of these rocks alone have been gradually produced to a much 

 greater depth than is to be observed in almost any other country. Soils 

 thus formed, in place, out of the rock strata on which they rest, are 

 called by writers Sedentary soils, and said to have usually little depth. 

 They are hardly known over the broad expanse of our continent north 

 and west of Kentucky, the whole of that extensive region being covered 

 by a mixed deposit of clay, sand, gravel, and boulders, called the 

 "Drift," made up of the debris of more northern rock strata, which have 

 been carried, during long periods of polar refrigeration by the immense 

 glaciers, which then covered a great portion of the Northern Hemisphere. 



This mixed deposit — made up largely of coarse and hard silicious 

 materials, which so covers the country of the great Northwest that 

 scientific observers of the North have asserted that the soil is not 

 affected by its underlying rock stratum — does not seem to have crossed 

 the Valley of the Ohio river to enter Kentucky. The southern ex- 

 tremity of the polar ice-field seems to have been near the line of our 

 latitude, and the great stream of water flowing from it, carrying its 

 gravel and sand, deflected by the river valley and by the elevated table- 

 land of our ancient rocks, was turned west of our State, leaving undis- 

 turbed and unburied the rich soil which had been produced in the long 

 period during which those rocks had been raised above the ocean level. 



