As indicated by the caption, this undated image shows an arched wall fountain that Jacques Gréber had intended to replicate for Clarence Mackay.
The caption accompanying this image reads as follows:
Jacques Gréber had intended to provide Clarence Mackay with an arched wall fountain like the one seen above, supplied for “Whitemarsh Hall,” by his accomplished father, Henri-Léon Gréber. instead, as many photographs attest, the similar space at Harbor Hill, remained vacant, until 1927!
See Harbor Hill, Clarence Hungerford Mackay's Mansion.