Kentish Ragstone is a hard, grey, sandy limestone that forms an important component of the Hythe Formation of the Cretaceous Period. The Hythe Beds are part of a suite of Cretaceous rocks that occur in the South East of England. The Hythe Beds were originally laid down as sediments in shallow seas some 110-115 million years ago. The Hythe formation also contains a softer sedimentary rock called Hassock which occurs in beds that alternate with those of the Ragstone. At Hermitage Quarry, the Hythe Beds attain a thickness of approximately 30m, with the Ragstone accounting for up to 60% of the total thickness.

Kentish Ragstone outcrops in various places, notably at the cliffs of Hythe and along the Greensand Ridge. Maidstone and Sevenoaks sit on Ragstone, where the Ragstone is of superior quality to that found in other areas of the Hythe beds. This is because the Ragstone beds are uniform in their lithology and present a continuous strata of fine grained grey or blue compact limestone.

Ragstone and Hassock occur in bands of between 15cm and 80 cm, and the difference in colour between them gives quarry faces a striped appearance. Hassock is soft sand and silt and the Kentish Ragstone is very hard and contains lime mud, sand, fossil material and glauconite, all cemented together - usually by the transparent mineral calcite.