The contact between them may be sharp, gradational, or erosional. The Redonda has gradational eastward transition into the upper Cooper Canyon Formation. The Milboro is gradational with the underlying Needmore Formation shale. Cuestas, homoclinal ridges, and hogbacks comprise a sequence of landforms that form a gradational continuum. The shale tongues typically have sharp basal contacts and gradational upper contacts. Their bases are sharp, but the tops are gradational. These rock types are commonly interbedded and gradational with each other. The contact between the two is gradational. Its contact with the overlying Espinaso Formation is gradational. Sand Formation is well defined in the southwest of East Sussex but is gradational elsewhere. In eastern New York, the contact between the Marcellus and Onondaga (where present) is gradational.