Maguayo Porphyry, and the Morovis/Ciales stock. Examples on Puerto Rico, all of Cretaceous age, include possibly the oldest bodies in the San Lorenzo batholith, the. The first group comprises small stocks, which have geochemical affinities with surrounding volcanic rocks of similar age. Plutonic rocks from the northeastern Caribbean can be subdivided into two distinct groups on the basis of their relationship with associated volcanic rocks. Five of the eight described echinoid genera from the Tertiary of PNG still live in waters of the Indo-Pacific today. nov., a temnopleurid echinoid Temnotrema macleayana (Tenison-Woods), a phymosomatoid echinoid stomechinid (?)gen. The fauna includes the clypeasteroid echinoids L. The rich echinoid fauna from the Lower Pliocene Kairuku Formation on Yule Island, Central Province, includes sea-grass meadow dwelling, and highly turbulent, shallow-water dwelling forms. Agassiz, 1898) and Brissopsis ?luzonica (Gray, 1851). Oligocene-Lower Miocene Padowa Beds in the Sagarai valley, Milne Bay Province, is dominated by sand and sandy-mud burrowing spatangoid echinoids Brisaster latifrons (A. The fauna from the Middle Miocene Langimar Beds at Aseki village, Morobe Province, is dominated by near-surface, sand dwelling clypeasteroid echinoids Echinodiscus bisperforatus Leske, 1778 and Laganum depressum Lesson in L. Tertiary echinoid faunas from four different environments are described from three localities in Papua New Guinea (PNG). The relevance of these observations to questions of equilibrium surface structure, epitaxial growth, and surface mass transport is considered. The relative areas of the (2 x 1) and (1 x 2) surface reconstructions at the extrema indicate that the step arrays introduce additional stresses into the surface. Large area islands and holes are also found on the extrema of gratings quenched from 1230^circC and are attributed to thermal fluctuations in the positions of steps at the extrema. The overall decay shape of the periodic step arrays under annealing is found sometimes to deviate from an ideal sinusoid-this deviation is most evident in the flattening of the extrema of the arrays and is associated with step contours that cross the extrema.
Step array surfaces quenched from 1230^circC exhibit similar structure. In the intervening angular range the surface is observed to undergo orientational phase separation.
The step structure on surfaces slowly cooled from 900^circC to room temperature are found to consist primarily of monatomic steps at misorientation angles less than 0.7^circ, while at angles greater than 1.6^circ a mixture of monatomic and biatomic steps is observed. The theory of the equilibrium step structure on Si is reviewed and models for the morphological evolution of surface step arrays are considered. The basic principle of STM and the particular experimental approach of this work are discussed. mass transport during the evolution of the surface toward equilibrium. The large-scale morphology of the step arrays was also studied to investigate features of. Regions of the periodic step arrays were examined to determine the equilibrium step structure for orientations up to 4^ circ away from (001) in the (110) zone. Periodic step arrays formed by grating surfaces on Si(001) were studied using scanning tunneling microscopy (STM) under ultra-high vacuum conditions.
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