During the summer of 1929 members of the International Summer School of Geology and Natural Resources, Princeton University, had the opportunity of examining with Mr. E. B. Bailey geological sections in the South-west highlands of Scotland and assisting in the determinations of tops and bottoms of beds in certain critical areas. The subdivision of the series into formations and the distribution of these formations were already for the most part known, but some important details of the structural interpretation were in doubt. In 1924, Thorolf Vogt, after visiting the area, stated that he had determined the order of succession in parts of the folded series; but these determinations by Vogt and their implications had not been verified or accepted by Mr. Bailey by the early part of 1929. Detailed observations made by the Princeton party in 1929, on strata which admitted of top and bottom determinations on the basis of cross-bedding, channelling and texture gradations, confirmed and extended the findings of Vogt; and Mr. Bailey is now in a position to restate the structural interpretation of the South-west Highlands making use of satisfactorily determined sequences in some of the units where formerly the sequence was in doubt or had been incorrectly inferred.