Gibraltar
from "Indus"
28 Sep * 58
* this does look like a £ as suggested by Annie, though it would make more sense if it was an abbreviation related to a date (presumably 1858) unless the artist was trying to sell the painting.

£58 is far too much to charge for an amateur work in the 1850s I would think.
Presumably the artist was on board the Indus when they did the painting. He could have been crew or a passenger.
I can see virtually no similarities in the two examples of writing, and would say they are definitely written by different people.
You say this is a two page watercolour? Is it loose within the book or attached at the spine? I am asking in case this watercolour was just put into the book for safe keeping and may not relate to the owner of the book.

Can I confirm that the rest of the pages in the book are blank?
Surrey may be a clue - you wouldn't expect something like that to travel too far. Though the book is very interesting it's monetary (and possibly sentimental) value is low.