Greetings Adam:
First, I do not appraise or value trees over the internet or via telephone. Appraisals must be conducted in-person and on-site.
Secondly, If the measurements you provided are indeed correct, then the tree you cut was not very large (i.e., circumference of 37" is equivalent to a tree barely 11.8" in diameter). Therefore, I'm assuming you meant to say 37" in diameter, not 37" in circumference. Obviously, terminology is very important considering a 37" circumference tree will contain very little volume, whereas a 37" diameter tree will contain a lot of volume!
If that is indeed the case, then the tree contained approximately 676 board feet (this is based on a sixteen foot log with a 30" diameter inside bark measurement). This board foot calculation is strictly ball-park as I have no idea of the "exact" dimensions of these two logs.
To estimate the value of the merchantable volume of this tree, simply multiply the merchantable board foot volume by the estimated black walnut value per board foot (refer to the following Timber Price Report):
http://web.extension.illinois.edu/forestry/il_timber_prices/pdf/itp_feb2010.pdf
Best of luck!
