What does fortune lies upon the surface of the earth as plentiful as the mud in our streets mean?

"Fortune lies upon the surface of the earth as plentiful as the mud in our streets" means that the gold that will transform the status of the nation is in much abundance and has become the subject matter as compared to mud in the streets.

Explanation:

The above statement was made by Horace Greeley during the gold rush. America, at that time experienced a transformation when gold was discovered.

By early 1849, it became a gold fever epidemic. There were discussions of gold almost in every corner of the nation. Young men saw that parting away with their wives that would be worth the hardship.

All these led to the statement of Horace Greeley the of New York Tribune:

"Fortune lies upon the surface of the earth as plentiful as the mud in our streets. We look for an addition within the next four years equal to at least One Thousand Million of Dollars to the gold in circulation."

if interdependence implies a two-way dependence, and if each partner is equally dependent on the other for success, then there is an equal commitment to the making the partnership successful. the advantage is sustainability of the relationship, the disadvantage is that decisions are "democratic" and therefore may take longer to reach and more likely to be a compromise (which is not always the best solution). as the interdependence moves away from equality, the decisions become more influenced by the more independent partner. in the extreme the relationship becomes more dictatorial and more like "master-slave". generally the relationship has less commitment in both directions and is more likely to be temporary.

if one generalizes (and one shouldn't), equity partnerships, which is probably what is implied by interdependence, can be slow to progress or change but durable. the extreme alternative, independent-dependent partnerships tend to be efficient but more fragile.

hope this but you will have to site your own evidence. : )