[PART 1. PREPARATION OF THE PHYSIOGRAPHIC DIAGRAM]
Several steps are involved in the preparation of a marine physiographic diagram. The raw data consist of continuously recorded echograms and lists of positions of the research ship. Echograms are profiles of ocean depth, automatically plotted against time (Luskin et al., 1954). The first step is to read and tabulate the depth at each peak, trough, or change of slope. These readings are plotted on a chart (1:1,000,000) as a series of closely spaced soundings. Depth profiles are plotted against distance at a standard vertical exaggeration of 40:1. The sounding lines are also plotted on a chart of small scale (1:5,000,000) which is at the same scale as the final physiographic diagram. The subsequent steps in the preparation of the diagram are illustrated by Figures 1a-d. The exaggerated profiles (1b) along the tracks (1a) show a succession of peaks and valleys. These features are sketched in along the tracks (1c). After all the tracks in a large area are sketched in this way, the major trends are estimated, and the diagram is completed by interpolation and extrapolation (Fig. 1d; Pl. 1). The vertical scale of the diagram is 1 inch = 5000 fathoms which is an effective vertical exaggeration of 20 to 1. The final diagram as printed is at a scale of 1:5 million at 40° N. on a Mercator projection.
There is a fundamental difference between the preparation of a terrestrial and a marine physiographic diagram. In the former the major problem is to select from more-detailed maps the features to be represented. Except in unexplored, inaccessible areas, the shape of all land features is a matter of recorded fact; the problem is to abstract and artfully draw the features in question. In contrast, the preparation of a marine physiographic diagram requires the author to postulate the patterns and trends of the relief on the basis of cross sections and then to portray this interpretation in the diagram.
PHYSIOGRAPHIC PROVINCE CHART: A study of the exaggerated profiles plotted during the preparation of the physiographic diagram revealed the existence of morphological features and morphological provinces not previously delineated. The limits of areas of contrasting morphology were noted on the profiles, and these points were plotted on a chart of small scale (also about 1:5 million at 40° N.) (Pl. 20).
CONTROL: Almost all the echo-sounding profiles used in the preparation of the physiographic diagram (Pl. 1) and the physiographic province chart (Pl. 20) were obtained by expeditions of the Lamont Geological Observatory and the Woods Hole Oceanographic Institution (Pl. 21). Some soundings were provided by the Hydrographic Department, British Admiralty (Pl. 21) and the International Hydrographic Bureau (Monaco).
Figure 1.—Method of preparation of physiographic diagram