This shows topsoil of 6-10 feet for areas of Manahtten.
http://www.farlang.com/gemstones/gra...-york/page_051
I knew it did not go very deep due to my readings of the construction of the subways. With areas that had little excavation I expect you could farm there after clearing.
What are you looking for in the way of cement production. I have mine/production locations that I can get to in a little bit. Unfortunatly I am reformatting my primary computer at the moment.