of an old term with a distinctly new meaning. For instance, it would be better to drop the term " fissure-veins" altogether than to apply it to something which would never have been so called by the classic authors who invented that term. But a mere restriction of the class, taking out deposits (shear-zones, etc.) which were once included in it, but leaving those which now, as always, properly belong to it, does not warrant the abandonment of the name. New births, of course, require new christenings; and the genealogies of science should not be confused by giving to the little strangers the names of their ancestors. There are some terms in modern geological literature which really ought to be followed by "Jr." But, on the other hand, when the ancestor still survives, albeit somewhat shrunken with age, he ought not to be mistaken for a baby, and re-baptized!

4. This leads me to say a final word concerning the classification of mineral deposits. The text offered for this symposium seems to me to be little more than a question of classification; and, after more than forty years of study, I am inclined to say, as Thackeray's Jeames Plush said of orthography, "As for classification, every gentleman has his own!"

For a logical classification requires a primary division, based upon the deepest and sharpest distinction that can be found, and a series of subdivisions, based upon less profound and, perhaps, less sharply defined differences-which should be, however, successively less important and duly subordinate to those which precede them. Moreover, the members of each rank should be equivalent in importance, as measured by the principle of the classification; and vagueness of distinction should be, if possible, confined to the last series (corresponding to I varieties" in biology).

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Now, in the classification of mineral deposits, we encounter at the outset the difficulty that the basis of the profound primary division depends upon the purpose of the classification. From the standpoint of the art of mining, perhaps the most radical distinction is between superficial and underground deposits; and classifications based on this distinction are doubtless most convenient for instructors in the processes and methods of

that art, who naturally follow this primary division with others based upon form, position, contents and structure, rather than genesis-which does not greatly concern the mining engineer, except so far as it may be a guide to the discovery, valuation and exploitation of mineral deposits.

On the other hand, a logical classification is conceivable from the standpoint of descriptive geology, arranging the deposits according to what they now are or contain, without primary distinctions as to how they acquired their present characteristics. Such a system might begin with a division into metalliferous and non-metalliferous deposits; or deposits in igneous, in metamorphic, and in sedimentary rocks; or deposits contained in the rocks of different formations.

No doubt the most scientific classification should be a genetic one; and for this purpose, probably the best practicable primary distinction is the one long ago proposed by Werner of Freiberg, between "contemporaneous" and "subsequent" mineral deposits. Yet it is conceivable that a still deeper and older distinction may be established hereafter, to which mineral deposits. like all other parts of the earth's crust, will be properly subject. Meanwhile, it seems to me that our classifications will continue for a considerable period to express the several purposes for which they are made, and the notions of the makers as to the relative general importance of the differences they represent; while the most important service that any investigator can render will be the accurate observation and adequate record of the facts required for larger induction and ultimate theory.

R. W. RAYMOND.

Structural Features of the Joplin District.

DISCUSSION OF PAPER BY C. E. SIEBENTHAL.

Sir:-Through the courtesy of Mr. Siebenthal I am given this opportunity of discussing the very interesting series of observations recorded in his paper on the "Structural Features of the Joplin District." As he has shown, the determination of the amount of faulting present in the Joplin district is a matter of considerable economic as well as scientific importance. The wide

divergence of opinion which has heretofore prevailed is somewhat more explicable in the light of Mr. Siebenthal's observations. In my own earlier work in the district, in 1900, I was led to believe in the presence of faults of one hundred to one hundred and fifty feet or more at a number of points. The reasons for this belief were essentially the same as might follow from a study of Mr. Siebenthal's sections I and IV if the intervening sections were absent. Very similar conditions were observed on the Continental tract, at Oronogo, at Aurora and elsewhere. With the clear evidence of faulting, the pronounced brecciation, the sheeting of the rock parallel to the contact and the very common coincidences of the fault with the boundary line and of the shale, there seemed no escape from the conclusion that certain shale patches at least occupied depressed areas due to faulting; this despite the recognition of the presence of a marked unconformity between the shale and the limestone and a great readiness to blieve in pre-Coal Measure erosion channels such as I had previously described in Iowa.1 The explanation was, however, unsatisfactory in one point which it was hoped later work might clear up. This was the exceedingly irregular distribution of the faults and fractures which could not be made to fall into any system. Neither did they seem to show any close relation to the larger structural features of the region. This difficulty is apparently to disappear as a result of the recent work. A great unconformity, partly due to land erosion and partly to underground solution, is quite adequate to explain any irregularity in the distribution of the shale patches, and, considering the weakness of the shales as compared with the limestones, it is clear that the great filled-in channels and sinks must have localized and controlled much at least of the minor and possibly some of the major deformation of the district. The boundary planes of these channels and sinks are the natural planes of readjustment, so that faulting relatively small in amount of throw, comes to assume all the appearance of major displacement. To one familiar with the methods of mine work in the Joplin district and the character of the ground, it will not be surprising that such phenomena have 'Iowa Geol. Surv., Vol. I., 169–179, Des Moines, 1893.

proven deceptive. The larger development of the sheet-ground in recent years has afforded the needed opportunity for correcting these false impressions.

Mr. Siebenthal has shown, I believe quite correctly, that many at least of the apparently heavy faults have only a slight throw and he has given such a reasonable explanation of the phenomena that the burden of proof is evidently upon us, if any there be remaining, who would still maintain a belief in faults of larger throw. Personally I must confess that such seem to me now to be exceedingly unlikely to be present, though they are far from impossible and it is quite true that there are differences in elevation of one hundred feet or more in identical beds of limestone within distances so short as to suggest step-faulting, at least rather than simple monoclinal folding.

In the matter of the bearing of these discoveries on the theory of the genesis of the ores I shall not at this time say much. While it is true that single faults of four to six feet are not likely to persist in depth two thousand feet or more, it is none the less probable, as it seems to me, that such zones of faulting as are present do break up and disturb the rocks sufficiently to establish a connection between the artesian waters of the Cambro-Ordovician and those of the Boone formation. Such a connection seems furthermore to be established by many independent facts of ore occurrence and association, and such a connection is all that is necessary so far as is concerned the theory of genesis put forward by myself and associates in the work of 1900.

H. F. BAIN.

REVIEWS.

The Geology of South Africa. By F. H. HATCH, Ph.D., M. Inst. C. E., president of the Geological Society of South Africa, and G. S. CORSTORPHINE, B.Sc., Ph.D., consulting geologist to the Consolidated Gold Fields of South Africa. Pp. xiv + 348; Plates I. with two colored geological maps and eightynine figures in the text. Macmillan and Co., London, 1905. The Macmillan Company, New York, 1905.

For some years an unusual interest has attached to geological conditions in South Africa. The immense output of diamonds from an increasingly large number of mines whose character is not duplicated in any part of the world and the extraordinary gold production of the banket reefs, as well as the prevalence of conditions which have thrown new light on the problems of glaciation are in part responsible for the large share of attention. which the technical and popular mind has bestowed on this region. The South African war, too, arresting as it did the rapid progress of economic development, served to emphasize the vast resources of the country.

The progress of mining exploitation has, however, been so rapid that geologic investigation has not kept pace with it and the inadequacy of published accounts of the geology has increased the natural tendency of the popular mind to look upon this country as a modern El Dorado.

The appearance of the GEOLOGY OF SOUTH AFRICA by two of the ablest of English investigators is therefore to be warmly welcomed by both geologists and technical men.

The volume comprises an introduction and six separate divisions. The introduction is divided into two parts, the first containing a full summary and discussion of all previous work by both private and official investigators. Their views are clearly and concisely stated and where later investigations have proved