another guide to determining soil type.
Guide to Texture by Feel | NRCS Soils
Once you start seeing rocks (glacial-till) then the good clay is not far below.
I would caution against digging a hole to the static water level (water table) chances are it wouldn't provide a source for water, but rather might work against you when the level drops...plus it could be quite costly depending on how deep a substantial water source is...
Are you getting any engineering assistance or is this on your own?