Pennsylvania Coal v Mahon (page 811)

Coal Company conveyed the surface of land to certain persons (“B) “but in express terms reserves the right to remove all the coal under the same and the grantee takes the premises with the risk and waives all claim for damages that may arise from mining the coal.”  (p. 811)
    
    [To understand the holding in Mahon, it is necessary to know that Pennsylvania recognizes three separate physical estates in real property – the surface estate, the mineral estate, and the support estate. The owner of the surface estate, as you might expect, acquires the right to possess and improve the surface of real property.  The owner of the mineral estate acquires the right to extract minerals from the property.  The owner of the support estate has the right to control the removal or non-removal of the layer of coal and earth that supports the surface.  Thus, when the owner of the mineral estate also owns the support estate, he has the right to extract coal without regard to whether it causes subsidence damage to the surface estate or any improvements thereon.
    
        Many years ago western Pennsylvania property owners severed the mineral estates and the support estates from the surface estates of much of the land in that region.  The coal mining companies typically acquired or retained both the mineral estate and the support estate.  Thus, coal mining companies owned the right not only to extract coal deposits from the land, but additionally to do so without any liability to the owners of the surface estates for damages resulting from subsidence.]