VERY little geological information appears to have been published on the State of Durango, in western Mexico. The observations therefore recorded during a brief journey by Dr. O. C. Farrington are of considerable interest (Field Columbian Museum, No. 89, geological series, vol. ii., No. 5). His route extended from the city of Durango, which is situated upon an alluvial plain hemmed in by low and rugged hills, to the silver-mining town of Villa Corona or Ventanas, distant about seventy miles in a direct line. The ground, which forms part of the interior plateau of Mexico, rises from about 6000 feet at Durango to 9000 feet. While large tracts of the area are semi-arid and sparsely covered with soil and vegetation, in some places corn is successfully grown, and elsewhere there occur extensive pine forests with oaks. Views of the scenery are given. Eruptive rocks prevail, and near the Ciudad ranch, on one of the highest parts of the plateau, there is a tract of weathered masses known as La Ciudad de Rocas (“The City of Rocks”). The outlines of the rocks are domed and rounded, and they appear to be due to the weathering of fairly homogeneous rhyolitic materials.