In case the difference in the character of a shallow surface soil and its subsoil should be unusually great, as may be the case in tule or other alluvial lands or in rocky districts, a separate example of that surface soil should be taken, besides the one to the depth of six inches. Specimens of salty or alkali soils should, as a rule, be taken only toward the end of the dry season, when they will contain the maximum amount of the injurious ingredients which it may be necessary to neutralize. Whatever lies beneath the line of change, or below the minimum depth of six inches, will constitute the subsoil. Should the change of color occur at a greater depth than twelve inches the soil specimen should nevertheless be taken to the depth of twelve inches only, which is the limit of ordinary tillage; then another specimen from that depth down to the line of change, and then the subsoil specimen beneath that line. Hilgard justly calls attention to the fact that all peculiarities of the soil and subsoil, their behavior in wet and dry seasons, their location, position and every circumstance in fact, which can throw any light on their agricultural qualities or peculiarities should be carefully noted and the notes sent with the samples. Unless accompanied by such information, samples can not ordinarily be considered as justifying the amount of labor involved in their examination. =57. Whitney=[40] suggests that a geologic map of the region to be sampled should always be at hand and that all samples should be rejected from spots showing local discrepancies, washings or other disturbances. The kind of analyses to which a sample is to be subjected also largely determines the method to be pursued in selecting it: For instance, a sample to be used for determining the size of the particles therein, may be taken in quite a different manner from that designed only for the determination of moisture. =58. In= the directions collated by Richards[41] and which have been largely followed by the correspondents of the Department of Agriculture, it is recommended to select in a field, four or five places, at least, per acre, taking care that these places have an homogeneous aspect, and represent as far as possible the general character of the whole ground. If the field, however, present notable differences, either in regard to its aspect or its fertility, the samples gathered from the different parts must be kept separate. The sampling of arable soil should be made only after the raising of the crop and before it has received any new manure. In other soils the sample should be taken only from spots that have not been cultivated.