SUMMARY AND CONCLUSIONS. 1241 



material for such ores will be the igneous rocks which in the future enter 

 the upper part of the lithosphere from the centrosphere. 



In conclusion the merits of the classification proposed may be sum- 

 marized as follows: 



First, the classification is strictly genetic, and is based upon a 

 consistent plan. 



Second, the primary divisions of metallic ore deposits are parallel with 

 those of rocks. Just as there are sedimentary, igneous, and metamorphic 

 rocks, so there are sedimentary, igneous, and metamorphic ores. If this 

 division of rocks be logical the division of ore deposits is equally logical. 



Third, the classification recognizes the gradation and connection 

 between different classes of deposits, one of the most fundamental laws of 

 geology. Recognizing that many ore deposits have a long complex history 

 in which many processes have been concerned, it makes the basis of the 

 classification the last process which resulted in the deposition of the ores 

 where they are now found. 



Fourth, it is believed that the classification offered, being strictly 

 genetic and recognizing gradation, is enlightening from a scientific point of 

 view and gives a better idea of the relations of various ore deposits to one 

 another than classifications heretofore proposed. 



Fifth, it is believed that the classification will assist mining engineers 

 and geologists in accurately describing deposits, and will give rules to 

 guide them in the exploration and exploitation of ore deposits. 



As an illustration of the practical usefulness of the classification is 

 the connection between genesis and depth for those ore deposits in which 

 descending waters were an important factor in concentration. Ores depos- 

 ited by ascending waters alone are likely to continue to great depth. 

 Therefore, where a given ore deposit has been shown to belong to this 

 class, the expenditure of money for deep exploration may be warranted. 

 Where a deposit is produced by descending waters alone the extent in 

 depth is probably much more limited. In such cases, when the bottom of 

 the oxidized product is reached, it would be folly to expend money in 

 deep exploration with the expectation of finding other rich oxidized masses. 

 Where the ore deposit belongs to the third class, that produced by ascend- 

 ing and descending waters combined, there is a rich upper belt which we 

 can not hope will be duplicated at depth. However, this class of deposit 



