(Found) One ocean with amphibious humans read in late 1970’s.

[Eric7512]

I read this book in the late 1970’s. The earth is one ocean with floating cities. There are humans that live on the floating cities and another species of humans that have evolved to live in the sea. I think the sea humans are called the ‘Seaborn Ones’. I do not remember the title. It was a paperback book written in English.

 

[Star-child]

Ascension Factor by Frank Herbert?

 

[Eric7512]

Ascension Factor by Frank Herbert?

Ascension Factor was written in 1988. I read the book I’m looking for in the late 70’s. But thanks for the suggestion.

 

[Danny McG]

I got a little tickle saying Robert Silverberg, something something darkness

 

[Bagpuss]

If it's Silverberg it could be: "Conquerors from the Darkness".

 

[Star-child]

Ascension Factor was written in 1988. I read the book I’m looking for in the late 70’s. But thanks for the suggestion.

Sorry.

 

[tachyon]

If not "Conquerors from the Darkness" perhaps it's Silverberg's earlier novella "Spawn of the Deadly Sea"

Science Fiction Adventures New Series v01n03 (1957 04) : Free Download, Borrow, and Streaming : Internet Archive

Science Fiction Adventures New Series v01n03 (1957 04)

archive.org

 

[Eric7512]

If it's Silverberg it could be: "Conquerors from the Darkness".

That is it!! Thanks, can’t wait to read it again.

 

[Danny McG]

I got a little tickle saying Robert Silverberg, something something darkness

Dammit!
That's what happens when I can't be bothered to look it up online, too many years since I read it to be positive in my answer