No. 6. DEPARTMENT OF AGRICULTURE. 183 



Geological Survey are numerous interesting statements concerning 

 the soils of various localities, considered particularly in relation to 

 their parent rocks, but thei^e observations have never been col- 

 lated for comparison, were not made according to a carefully pre- 

 pared system of observation, and, commonly, afford little informa 

 tion concerning the agricultural relations of the respective soils. 

 The Experiment Station has found its funds altogether too limited 

 to undertake a systematic soil survey of the State, aud has been 

 obliged to limit itself to such casual examinations as could from time 

 to time be made in the study of various local problems. Within 

 very recent years the Bureau "^of Soils of the United States Depart- 

 ment of Agriculture has mapped the soils of several counties — 

 Adams, Montgomery, Chester, and parts of Lancaster, Lebanon, 

 Dauphin and Clinton. The "surveys mada by the bureau classify 

 soils primarily upon very broad geological aud physiographical rela- 

 tionships, and, secondarily, upon textural characters of surface and 

 subsoil, with scant attention to the mineral and chemical composi- 

 tion of the various soil classes. The reports of these surveys thus 

 far published exhibit thirty-six distinct soil classes. ^Yhen the 

 western and northern parts of the State shall have been mapped, 

 a large addition to the number of types will appear, probably sim- 

 ilar, most of them, to the types found in the regions of Ohio and 

 New York thus far mapped. 



In considering how to select and shape the materials at command. 

 BO that they may best serve your purposes as instructors in the 

 theory of practice of agriculture, I have decided to bring to your 

 attention some of the problems with which the soil chemist 

 is wrestling, using Pennsylvania data for illustration, so far as they 

 piove fit. 



By way of introduction to these problems, let us take a bird's- 

 eje view of the manner in which our soils have been formed. Their 

 ancestral rocks Avere great crystalline masses, made up chiefly of 

 silicates of potash, soda, lime, magnesia, iron and aliimnia, with 

 small but well-distributed amounts of pliosphates of lime, iron and 

 alunmia, and otlu-r cempounds aud elements. These formed the 

 backbone of the new continent lifted above the waters of the ocean. 

 Its rocky surfaces were riven and powdered by the summers' heat 

 and winters' frost, with their alternate expansions and contractions. 

 The winds carried from place to place the dust thus formed, riv- 

 ulets gathered up the loose fragments, rolled the angular stones 

 into round pebbles, and, using the rolling and suspended rock frag- 

 ments as abrasive agents, became a liquid sandpaper, scouring and 

 indenting the rocky stream beds, and finally in the lowlands widened, 

 dropped the coarse sand, then the fine clay, and poured into the 

 ocean basins. The rains filled the rock pores, formed new, hydrated 

 minerals of enlarged volume, promoted the oxidation of metallic 

 elements, and, finally, with the aid of the carbonic acid of the atmos- 

 phere, slowly broke up the silicates, dissolved and carried away the 

 chloride of soda, potash and magnesia, and the carbonates of lime and 

 magnesia, and delivered them to the ocean, leaving on the land sur- 

 faces, finely divided rock debris, of which the silica and other in- 

 soluble substance formed a larger proportion than they presented in 

 the newly exposed rock masses. Presently the carbonate of lime 

 v=ud magnesia formed in the shallows of the ocean waters great beds 

 Ot ooze, molluscan shells and coral reefs, more or les« mixed with sand 



