Analysis of Sonnet LV

SO oft as I her beauty doe behold,
And therewith doe her cruelty compare:
I maruaile of what substance was the mould
the which her made attonce so cruell faire.
Not earth; for her high thoghts more heauenly are,
not water; for her loue doth burne like fyre:
not ayre; for she is not so light or rare,
not fyre; for she doth friese with faint desire.
Then needs another Element inquire
whereof she mote be made; that is the skye.
for to the heauen her haughty lookes aspire:
and eke her mind is pure immortall hye.
Then sith to heauen ye lykened are the best,
be lyke in mercy as in all the rest: