Within the extensive plateau crossed by the upper Miño there are a vast number of tumuli. Their distribution is fairly homogeneous and they reach densities of up to 6 mounds per km 2. The grave goods recovered from some of these monuments bear little relation to those in the coastal areas, especially so by the later par! of the 3rd millenium BC. Recent surveys have found that some of the bigges...

Located near the edge of the Pacific coastal plain in the far southeastern corner of Chiapas, Mexico, is the large pre-Columbian ceremonial center known as Izapa. Situated on the terrace of a small stream tributary to the Rio Suchiate, the border river between Mexico and Guatemala, the site consists of more than 130 mounds sprawled over several hectares of lush tropical lowland at the base of t...

Droughts are increasing in severity and frequency, yet the mechanisms that strengthen ecosystem resilience to this stress remain poorly understood. Here, we test whether positive interactions in the form of a mutualism between mussels and dominant cordgrass in salt marshes enhance ecosystem resistance to and recovery from drought. Surveys spanning 250 km of southeastern US coastline reveal spat...

We formulate and implement a generalized island-dynamics model of epitaxial growth based on the level-set technique to include the effect of an additional energy barrier for the attachment and detachment of atoms at step edges. For this purpose, we invoke a mixed, Robin-type, boundary condition for the flux of adsorbed atoms (adatoms) at each step edge. In addition, we provide an analytic expre...

Vernal pools are seasonal wetlands that harbor rare and endemic plants and animals. In California, vernal pools are often associated with Mima mounds, roughly circular soil mounds, found in grassland landscapes. The processes that form and maintain the mound-pool complexes have not yet been conclusively identified, even though such information is necessary to understand the effects that land us...

RÉSUMÉ Claude Lalou, Évelyne Brichet, Héloise Pérez-Leclaire Centre des faibles radioactivités, Laboratoire mixte CNRS-CEA, Domaine du CNRS, 91190 Gif-sur-Yvette, France. Received 8/7/83, in revised f orm 20/2/84, accepted 20/2/84. Using uranium series disequilibrium and oxygen isotope stratigraphy, a chronology has been established for the different events which led to the formation of the hyd...