Caption: View Petrified Forest, Lithodendron Wash, Apache and Navajo counties, Arizona. Fort Defiance quadrangle. Chinle formation. August, 1913.
The above photo shows scattered petrified logs from a portion of Petrified Forest National Park known as the Black Forest. This photo was taken by the famous American geologist Herbert E. Gregory during the course of research, which resulted in his 1917 report that first named the Chinle Formation (Gregory, 1917).
This photo is available at the U.S. Geological Survey online photographic library and is one of 223 photos of the Chinle Formation. Some of these photos have previously been published in USGS publications; however, many of them are still unpublished. Over 100 photos are from Gregory's important Chinle work from the early to mid 1900s. Old photos are an indispensible resource when conducting stratigraphic work as it allows the stratigrapher to view key outcrops which were important to the original studies. Before the advent of point and shoot and digital cameras a lot of work went into taking and developing photos and therefore sites were only photographed when they were of some importance.
Jeff Martz has already discussed (scroll down past the giraffe and donkey part) the importance of photographing key stratographic sections, labelling them, and publishing them in order to allow future researchers to replicate and test your work. We are currently dealing with the frustrating task of trying to relocate key Chinle sections (type sections) in order to match them with our current work. Unfortunately the original publications provide only vague directions to and descriptions of these outcrops and more recent workers who claim to have relocated the sites (and measured sections there) have published data not only with geographical errors but also with measured sections that do not even come close to matching the original descriptions (more on some of these in future posts, maybe they thought no one else would ever check?).
To close, here is another classic H.E. Gregory photo. "Division C" was later formally named the Petrified Forest Member (Gregory, 1950).
Caption: Chinle formation, Division C, Chinle Valley, near Round Rock. June, 1913.
Gregory,H. E. 1917. GeologyoftheNavajo Country -a reconaissance of parts of Arizona, New Mexico. and Utah: U.S. Geological Survey Professional Paper 93, 161 p.
Gregory, H.E. 1950. Geology and geography of the Zion [National] Park region, Utah and Arizona: U.S. Geological Survey Professional Paper, 220, 200 p.
in The Biology Files