Not P but Moby-Dick (4)

[Mike Jing]

The following excerpt is from Chapter 16:

still, from the audacious, daring, and boundless adventure of their
subsequent lives, strangely blend with these unoutgrown peculiarities, a
thousand bold dashes of character, not unworthy a Scandinavian sea-king, or
a poetical Pagan Roman. And when these things unite in a man of greatly
superior natural force, with a globular brain and a ponderous heart; who
has also by the stillness and seclusion of many long night-watches in the
remotest waters, and beneath constellations never seen here at the north,
been led to think untraditionally and independently;

What does "globular" and "ponderous" mean here?