Field studies of the Cambrian rocks in northwestern Montana were begun in 1931 when C. H. Clapp and the writer were mapping the areal geology of the Coopers Lake quadrangle for the Montana Bureau of Mines and Geology. At that time only two sections of these Cambrian rocks had been published, one from the Dearborn River (Walcott, 1908c, p. 200–203), and the other from Gordon Mountain (Walcott, 1917b, p. 16–19). It soon became clear that, with the possible exception of the Flathead and Wolsey, the Cambrian formations in the Three Forks (Peale, 1896), Little Belt Mountains (Weed, 1899), and Philipsburg (Calkins and Emmons, 1915) quadrangles had no readily recognizable lithologic equivalents in northwestern Montana. Fossils had not been found, and detailed sections of these rocks were unmeasured. Consequently, further mapping could not be done accurately until at least the major details of the Cambrian stratigraphy were understood.
Data for the solution of at least six important problems were needed. (1) Which Cambrian series are represented in northwestern Montana? (2) What is the total thickness of the Cambrian rocks, and what is the thickness of those in each series represented? (3) Are unconformities or disconformities present, and if so, what is the magnitude of each? (4) What are the important lithologic characteristics of the Cambrian sediments within the area? (5) What are the persistent lithologic units which can be used as mappable formations? (6) What faunas do the sediments contain?
During the summer of 1932, nine detailed sections were. . .