WTF?
What is it you want to know?
However our friend Alberich has brought up a very interesting point about the voice that was so admired and exclaimed. When Marian Anderson was popular, so were big vibratos--just as there were periods of time where a virtually vibrato-less voice was considered ideal. . Add the fact that Anderson was a classically trained contralto--a voice type not widely heard in classical music any more. A lot of contralto music is sung these days by mezzo-sopranos whose timbres will be somewhat brighter than the darker "heavy-ish" tone of a true contralto even if the ranges of the two voice types may be similar. You even hear more countertenors singing "alto" parts than you do contraltos.
Even so--modern contraltos still tend to have less of a prominent vibrato than in Anderson's day.
Example--contemporary contralto Nathalie Stutzmann:
http://www.youtube.com/watch?v=-Yq04mGvKl0
Compare the same aria sung by Marian Anderson (even taking in consideration the quality of sound recording at the time)
http://www.youtube.com/watch?v=14MwxfiPHVY
Here are two celebrated contraltos that were roughly contemporaries of Anderson's, also singing "Erbarme Dich"
Kathleen Ferrier:
http://www.youtube.com/watch?v=jh_1CKyZVSc
Eula Beal:
http://www.youtube.com/watch?v=gIdNBgyC88o
This is British contralto Clara Butt (couldn't find the Bach, but this still will demonstrate a very fast and prominent vibrato):
http://www.youtube.com/watch?v=XX4fEC_zwck
It actually takes a lot of listens before we can get passed the "oddness" of these voices and appreciate why these singers were so highly thought of.
As a contrast, mezzo-soprano Marilyn Horne:
http://www.youtube.com/watch?v=LJ6SxpwzhSU
And a countertenor Michael Chance (even though I can appreciate the artistry and beauty in his voice and interpretation--I still feel a bit disturbed by it).
http://www.youtube.com/watch?v=dHbOOe8n2gY
Since I have no idea what it is you really want to know about Marian Anderson, I will also post these websites where you can read all about her:
http://www.mariananderson.org/
http://www.library.upenn.edu/exhibits/rbm/anderson/
http://www.npr.org/artists/102980721/marian-anderson