he undertakes. From the reports of the areas surveyed with reasonable exactness and care, each citizen is able to make out just what not to expect, before beginning to prospect. When the researches are conducted in a systematic way over more or less extensive areas and under governmental auspices the work becomes "geological surveying" in contra distinction to private "expert" work. The primary objects of state surveys is to obtain a comprehensive insight into what the commonwealth has in natural resources, to take an inventory of the natural possessions of the district, and to set forth to the public accurate and reliable descriptions of the mineral contents. Accounts of this kind are eagerly sought after, not only by the citizens of the state but by many others outside, those residing in other states and foreign countries. The benefits arising are three-fold. To the land-owners it is of direct benefit in placing a substantial and increased valuation on the tracts surveyed; to the citizens at large is an encouragement to the further development of the region, and a stimulus to all industrial activities; to the investor, either at home or abroad, it is an authoritative guaranty, protecting him from the wiles of nomadic speculators, making him feel more secure in making investments and therefore more ready to advance a much higher rate than he otherwise would feel justified in doing.

In all economic geological inquiry the work divides itself naturally into two classes both of which, while apparently sometimes covering the same ground, are very different. They form rather two parallel lines of investigation which supplement each other so that nowhere is there a duplication of efforts. One of these liaes considers a particular deposit for an entire province, and is commonly denominated subject work. The other treats of all deposits of a useful character which are found in a given district and is technically termed areal work. Reports on counties, "sheets," or other limited districts are results in areal work. The former is a consideration of the properties, uses and methods of development, of the manipulation of the different deposits and the kinds occurring in the various localities. The second notes the extent, adapt

ability and accessibility of deposits as found in particular places.

The work of the earlier geological reconnoissances was a mixture of the areal and the subject, reports on the county being the most common unit as the basis of presentation. But the reports of a quarter of a century ago were very different from those of the present day, and in most places were largely preliminary, especially in this country. They differ from the modern areal reports in embracing also much general matter and thus to some degree they covered both fields, but neither of them fully. Furthermore, natural history was commonly included and this took up no small part of the means and efforts. The areal reports of to-day are confined almost entirely to the mineral resources. They are very much more extensive and much more practical than the earlier accounts. Detailed information of a local character is considered; the present and possible future developments of the mineral wealth are set forth. Its direct purpose is to satisfy constant and every increasing demands for reliable information in regard to given localities. The desire to know about the mineral products of each particular neighborhood is so general that full details are required concerning every substance which is, or is likely to be of value, to the land-owner, or occupant, in the district. Probably one half of the people making inquiry seek information of a local character. The disemination of useful information regarding particular districts is accomplished in three ways; first by descriptions and sections; second, by illustrations; and third, by maps. No less than three-fourths of the geological facts are recorded cartographically. In consequence, therefore, a modern geological map is a graphic summary of a vast amount of useful information. In addition to an accurate representation of the ordinary geographical features, as in the best atlases, a properly constructed geological map records much more. On it are indicated, within a few feet where the topography is represented properly, the elevations above the sea level of every point within the borders of the area; the drainage basins and the water powers; the distribution and limits of the different

geological formations, the various kinds of ores, building stones, clays, and all minerals of economic value contained in the several beds, as well as the best places for obtaining all of these substances. The map also forms a reliable soil index, which, with some additional explanation, serves also as a guide to the distribution of the forests and plants generally.

But all the districts considered cannot be treated alike in the mapping. Some places require far more work than others, either on account of the great importance of the mineral deposits or the natural difficulties caused by the ruggedness of the country. Other regions, as those which contain the principal iron ores, the most valuable lead and zinc deposits, or particular coal beds, require, in the beginning, accurate relief maps. Places where the immediate mineral wealth is not so great do not require so elaborate topographical maps. At the present time it is not advisable nor, even if it were desirable, would the resources of a state survey permit it without a very considerable enlargement of its powers. The work goes on as rapidly as is consistent with good and accurate results. In order of their importance must the various districts be mapped and in proportion to their natural wealth should the detail be recorded.

The preparation of a full set of maps of this kind is not the result of few day's effort, but of the labor of years. As a part of the systematic investigations carried on in regard to economic resources there should be prepared a series of maps which would embrace for every section of the district all of the information mentioned. Some of them need to be somewhat general in their character and ordinarily accompany the different special reports. Others should be more detailed in their make-up and cover given counties or such other areas as may be thought desirable. In the construction of maps showing the distribution and occurrence of mineral substances it is of prime importance that the surface relief should be depicted. in a readily intelligible manner. One which represents most closely a perfect miniature of the surface of the region is far superior to any ordinary atlas. It is invaluable not alone to the trained geologist, but it is about the only practical way by

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which the average citizen is able to comprehend, at a glance, the explanations. In proportion as the exactness with which the diminutive representation approaches the actual surface, in the same proportion does the usefulness of the work increase. The modern methods of making maps are so far advanced over those of a quarter of a century ago that it enables them to be made at a cost within the reach of all.

In brief, then, a properly constructed geological map of a district not only locates accurately the various mineral deposits, but also represents the prominent landscape features by which the locations may be more readily recognized. A relief map also served other purposes. Upon it may be based models of the more important districts which are to be taken as characteristic of much larger areas and which are to represent in a graphic manner the structure, arrangement and relations of deposits. Eventually a relief model of the entire district may be constructed on a suitable scale. Besides, for the purposes mentioned it would afford one of the most instructive objects for presenting to the pupils of schools the geographical features of their state. With the wide introduction of the new methods of teaching geography the value of such aids cannot be overestimated.

The scope and aims of areal and subject work are quite different. The ground covered by the former has been outlined. The latter is primarily to satisfy a wide and ever increasing demand for information in regard to the existence, mode of occurrence, properties and commercial values of the various substances. Such deposits are not limited by ordinary political boundaries, but each kind of mineral, clay or other mineral product dug from the earth belongs to some particular geological formation; in other words, it is found at some horizon or level more plentiful than at others. Thus, one formation is abundantly supplied with coal; another with ores of zinc or lead; a third with materials for the manufacture of cements; and others with still different substances of economic value. Each is found in a particular geological zone and rarely or very sparingly elsewhere. Only within certain districts

would search for a given substance be successful; outside of these areas no amount of prospecting would ever disclose the material sought. When the information is obtained concerning any particular mineral substance the entire subject must be carefully considered. At the outset a clear understanding of the geological structure of the rocks containing it is of prime importance. The localities where it occurs require description. The arrangement, relations and extent of the deposits must be defined; the origin and properties discussed; the accessibility and value determined; the uses of the substances, the nature and status, both present and probable future of the industries connected, fully considered. A complete report on each special subject is therefore comprehensive in character and concise in statement. The work cannot be weighed with the details of only local interest, as this would extend the account far beyond the space that could be alloted to it. Information of an entirely local character must be recorded largely on maps or described in accounts of areas.

The neccessity of a dual arrangment of work in completing a thorough geological survey is obvious. On account of the magnitude of the work the investigations must necessarily extend over a period of years. The means usually provided by a province are far too inadequate to extend the detailed work over a whole state in a single year, and consequently in the beginning of the work some areas must be taken up first and finished, before others can be inquired into and mapped in detail. At the same time the work on various topics may go on over the whole region and the results of the investigations on the various deposits published and given to the public long before all the work of all of the counties or districts is done.

As the outcome of work done in important mining districts the accompanying volume comprises the areas covered by sheets one to four, and is the first of the series of reports on areal geology, issued by the Missouri Geological Survey.