At-what-depths-can-you-detect-a-change-in-coloursize-of-the-soil-strate-observed-during-the-drilling-of-the-borewell

For instance the top 10 -20 feet would be the top soil and would be dark reddish brown color while at depths beyond 20 ft, the color could change to light brown or greyish. Any pictures taken during the drilling would be awesome!