from an early date, geologists have struggled to explain the presence in nevada and adjacent areas of the antler orogenic deposits without achieving a consensus. the advent of plate tectonic theory provided a variety of possible mechanisms by which the roberts mountains thrust and the orogenic deposits could be explained, but none of them has been universally accepted. as outlined in the following paragraphs, plate motion along the western margin of the north american continent in the late devonian has been offered as the cause of the orogeny and three varieties of it have been tried—east dipping subduction, west-dipping subduction, and strike-slip motion. none of them is without serious problems and the nature and driving force of the orogeny remain uncertain.