154 sets of drill cuttings recovered from Zinc Corp.'s stratigraphic / exploratory well Lake Cootabarlow bore no. 2 over successive 10 foot hole depth intervals were examined for their microfossil content by the SA Government's palaeontologist, who made the following findings: Sediments of the Great Artesian Basin portion near Lake Cootabarlow were deposited on 'basement' sandstones and quartzites of unknown age, and comprise three distinct series: 1) lacustrine strata, from surface to 750 feet hole depth; 2) marine strata, from 750 to 1390 feet; and 3) lacustrine strata, from 1390 to 1470 feet. Only the marine series are fossiliferous, the foraminiferal assemblage being arenaceous in character. No zoning was apparent, but correlation has been made with the Roma Series of Queensland, which have been placed in the Aptian stage of the Lower Cretaceous by Whitehouse. There is evidence of a stratigraphical break between the lower lacustrine beds and the marine series, but not of a similar break between the marine and upper lacustrine series; the change in this case being transitional in character. Although lithologically the upper lacustrine sediments appear similar to those of the Winton Series, which are normally regarded as Upper Cretaceous, the suggestion is made that the lithological character of sediments is the result of their environment, so all of the Winton beds were not necessarily deposited at the same time. In accordance with this viewpoint, the writer places the upper lacustrine series as Mid-Cretaceous, probably Albian. The lower lacustrine sediments onlap the 'basement', and can be tentatively placed in either the Upper Jurassic or Lower Cretaceous, there being no microfossil evidence in them to decisively determine their stratigraphic position.