William John Sinclair (1877–1935) was a geologist and vertebrate paleontologist, noteworthy for his collaboration with Walter W. Granger on stratigraphy in New Mexico and Wyoming.
[2] Granger's early collaboration with Princeton geologist and paleontologist William J. Sinclair produced a series of detailed and perceptive stratigraphic contributions.
This research, published primarily in the years 1911–1914, established the first mammalian biostratigraphy of the Paleocene-early Eocene of the San Juan Basin, New Mexico and of the Eocene of the Bighorn and Wind River basins in Wyoming.
[1]In 1920 he started a major study of the fossils and geology of the lowest beds of the Brule Formation in the Badlands, then called the red layer.
He carefully recorded the vertical positions of the fossils within the lower Brule Formation and documented changes in the fauna.