Defoe's novel

Hi, I was reading a book by Defoe I encountered the paragraph below, could you answer my questions seen in the brackets)

In one
place in particular we saw the head of an elephant, with several teeth
in it, but one of the biggest that ever I saw; the flesh was consumed,
to be sure, many hundred years before, and all the other bones; but
three of our strongest men could not lift this skull and teeth; the
great tooth, I believe, weighed at least three hundredweight; and this
was particularly remarkable to me, (I: what is that was "remarkable") that I observed the whole skull was
as good ivory as the teeth, (I: whole skull was made of same substance of ivories? same?) and, I believe, altogether weighed at least
six hundredweight; and though I do not know but, by the same rule, all
the bones of the elephant may be ivory, yet I think there is this just
objection against it from the example before me, (I=?) that then all the other
bones of this elephant would have been there as well as the head.