The coarse ferruginous sands at the base of the Cretaceous series, in the countries of Bedford and Cambridge, have of late years attracted considerable notice, not only as sources of iron ore, but also of phosphatic matter. To these deposits the attention of geologists has been directed, and among other valuable papers, may be mentioned some by Messrs. Seeley and Walker,1 who have treated of their general physical characters, and also of their interesting fossil contents. It may be useful to some of the readers of the Geological Magazine, who are interested in tracing out the range of this deposit, and the peculiar conditions under which it was accumulated in some parts of the area, to point out briefly its characters and contents in the adjoining county of Buckingham; i.e., around Aylesbury: more especially so, as these sands have been considered to be partly equivalent in time, or the marine conditions of the Wealden and Purbeck strata.