17-1800's
I know that James Hutton is considered a father of modern geology and he was born during some where in the 1720's so that's the closest answer, also Charles Lydel was born during the late 1790's.
35.5 degrees.
Explanation:
ACB = 1/5 of AOB
Plug in 61 degrees for AOB.
1/2 of 61 = 35.5.
If not correct, then you may correct me.