Describe symbolism in The Log from the Sea of Cortez by John Steinbeck

From the text:

"For the ocean, deep and black in its depths, is like the low dark levels of our minds in which the dream symbols incubate and sometimes rise up to sight like the Old Man of the Sea. And even if the symbol vision be horrible, it is there and it is ours. An ocean without its unnamed monsters would be like a completely dreamless sleep."