The Eastern Hemlock is very slow growing, can live for hundreds of years, and can reach 6' in diameter, but I've never seen one that big.
The Catskill Mtns were almost all Hemlock, but during the Civil War they were clear cut as the tannic acid was used for leather tanning for the war effort. Hardwoods grew in their place.
It was often used for barn siding, as it would not rot if it were not touching the ground. Lots of barns lasted over 100-year-old, and it did not need to be stained or painted. The farmers liked that, because unfinished barns were taxed at a lower rate.
My cousin says it gets harder with age because it absorbs the minerals from the rain water. When their barn fell down, he started making large picture frames from the siding. (which I've also seen in several restaurants around here).
Now it seems that every trendy restaurant in sight has re-purposed barn siding. The workmanship is often horrible, but since it is re-purposed rough wood, no one seems to notice.