Passing.

Edward Sheriff Curtis, The Vanishing Race

The passing of every old man or woman means the passing of some tradition, some knowledge of sacred rites possessed by no other...consequently the information that is to be gathered, for the benefit of future generations, respecting the mode of life of one of the great races of mankind, must be collected at once or the opportunity will be lost for all time.
- Edward Sheriff Curtis

In Mr. Curtis we have both an artist and a trained observer, whose pictures are pictures, not merely photographs; whose work has far more than mere accuracy, because it is truthful.…Mr. Curtis, because of the singular combination of qualities with which he has been blest, and because of his extraordinary success in making and using his opportunities, has been able to do what no other man ever has done; what, as far as we can see, no other man could do. He is an artist who works out of doors and not in the closet.…He has lived on intimate terms with many different tribes of the mountains and the plains. He knows them as they hunt, as they travel, as they go about their various avocations on the March and in the camp. He knows their medicine men and sorcerers, their chiefs and warriors, their young men and maidens…
- Theodore Roosevelt

A tribal-categorization of the Edward Sheriff Curtis portfolio can be found here.