What will be pronounced strange or curious is largely determined by the range and composition of the common body of knowledge to whose laws and uniformities the phenomena in question apparently fail to conform. What is passing strange to one generation may become easily intelligible to the next. We all have eyes that see not for all but a limited range of facts and views; and we unconsciously fill out the blind-spots of our mental retinæ according to the habits and acquisitions of the surrounding areas. We observe and record what interests us; and this interest is in turn the outcome of a greater or lesser endowment, knowledge, and training. A new observation requires, as a rule, not a new sense-organ or an additional faculty, nor even more powerful or novel apparatus, but an insight into the significance of quite lowly and frequent things. Most of the appearances of the earth's crust, which the modern geologist so intelligently describes, were just as patent centuries ago as now; what we have added is the body of knowledge that makes men look for such facts and gives them a meaning. And although "the heir of all the ages," we can hardly presume to have investigated more than a modest portion of our potential inheritance; future generations will doubtless acquire interests and points of view which will enable them to fill some of the many gaps in our knowledge, to find a meaning in what we perchance ignore or regard as trivial, and to reduce to order and consistency what to us seems strange or curious or unintelligible. And future generations, by virtue of a broader perspective and a deeper insight, may give little heed to what we look upon as significant,--much as we pronounce irrelevant and superstitious the minute observances whereby primitive folk strive to attract the good fortunes and to avoid the dangers of human existence. I