The Great Gatsby, solid Americans

Could you please tell me if "solid" in this passage from the chapter Three of The Great Gatsby means "robust" (physical sense) or "respectable" (moral sense)?

I was immediately struck by the number of young Englishmen dotted about; all well dressed, all looking a little hungry and all talking in low earnest voices to solid and prosperous Americans. I was sure that they were selling something: bonds or insurance or automobiles. They were at least agonizingly aware of the easy money in the vicinity and convinced that it was theirs for a few words in the right key.

Thank you.