A hundred feet of tree, the old pine's top half, lay partly submerged in our shallow cove.


That is from Stephen King's Mist.....

The pine tree was actually 2 hundred feet tall?

It's hard to believe for a pine tree to be 200 feet tall......
Hi Pructus
The sentence doesn't say exactly how tall the tree was, but presumably the height was well over 100 feet. (The White Pine, for example, can grow to 150 feet or more.)
If I were to say "the old pine's top half", the word 'half' would not be intended as a precise measurement. Instead, I would be referring to the top part of the tree, and I would be approximating that the top part was at least half (but probably less than three quarters) of the total height of the tree.
I don't quite understand how the top half was submerged in whatever and not the lower one ... Was is horizontal, was the tree felled?
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Thanks Yankee!!!
 Marius Hancu's reply was promoted to an answer.
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My presumption was that the tree had fallen (for whatever reason), and the top of it landed in the water. I've seen trees laying in a river (or some other body
of water) before.