“The prevailing soil type is what would be called a loam,” said Percy, “and a single set of composite samples will fairly represent at least three-fourths of the land on this farm.

“It seems to me that it is enough for the present to sample this prevailing type, and later, if you desire, you could collect samples of the minor types, of which there are at least three that are quite distinct.”

“A loam soil is one that includes a fair proportion of the several groups of soil materials, including silt, clay, and sand.”

“What is silt?” asked Mr. Thornton.

“Silt consists of the soil particles which are finer than sand,—­too small in fact to be felt as soil grains by rubbing between the fingers, and yet it is distinctly granular, while clay is a mere plastic or sticky mass like dough.  What are commonly called clay soils consist largely of silt, but contain enough true clay to bind the silt into a stiff mass.  In the main such soils are silt loams, but when deficient in organic matter they are yellow in color as a rule, and all such material is usually called clay by the farmers.”

“Well, I had no idea that it would take us a whole day to get enough dirt for an analysis,” remarked Mr. Thornton, as they were collecting the samples late in the afternoon.  “Five minutes would have been plenty of time for me, before I saw the holes you’ve bored to-day.”

“The fact is,” replied Percy, “that the most difficult work of the soil investigator is to collect the samples.  Of course any one could fill these little bags with soil in five minutes, but the question is, what would the soil represent?  It may represent little more than the hole it came out of, as would be the case where the soil had been disturbed by burrowing animals, or modified by surface accumulations, as where a stack may sometime have been burned.  In the one case the subsoil may have been brought up and mixed with the surface, and in the other the mineral constituents taken from forty acres in a crop of clover may have been returned to one-tenth of an acre.”

“Certainly such things have occurred on many farms,” agreed Mr. Thornton, “and they may have occurred on this farm for all any one knows.”

“Fifty tons of clover hay,” continued Percy, after making a few computations, “would contain 400 pounds of phosphorus, 2400 pounds of potassium, 620 pounds of magnesium, and 2340 pounds of calcium.”

“I don’t see how you keep all those figures in your head,” said Mr. Johnston.

“How many pounds are there in a ton of hay?” asked Percy.

“Two thousand.”

“How many pounds in a bushel of oats?”

“Thirty in Virginia, but thirty-two in Carolina.”

“How many in a bushel of wheat?”

“Sixty”

“Corn?”

“Fifty-six pounds of shelled corn, or seventy pounds of ears.”

“Potatoes?”

“Eighty-six pounds,—­both kinds the same, but most States require sixty pounds for the Irish potatoes.”