 In 1956 Rendall published "Mollusca Orcadensia", a paper which brings together from all available sources records of marine mollusca indigenous to Orkney, which he had commenced in 1916.He published "Orkney Shore", a work on the seashore life of Orkney, in 1960.It has been said, "All his studies -
whether scientific, archaeological, theological or literary - were rooted in Orkney, and
a love of the islands drove the rigour which he applied to each of his chosen areas".