To the west of Los Angeles, now chiefly within the city limits, lies a comparatively level plain. In the midst of this plain was discovered by the writer and others the most remarkable deposit of prehistoric animal remains ever unearthed: — great in variety of species of plants, birds and mammals; enormous in quantity, perfect in preservation in a matrix of tar, and unique in the methods of accumulation. <br /><br />Literature is not wanting in description of the species of animals and plants found in these beds, but the methods of accumulation have received little publicity in print. Two methods have been proposed, one known as the "trap" method and the other, the "drift" method. The evidences of the latter so far as the writer is aware, have not been given except in his early lectures before scientific societies and to visiting scientists. <br /><br />The trap method of accumulation considers that the animals were caught by accident in the tarry mass in their passing, or by sinking while drinking of the shallow water in the pool or eating of the scanty vegetable growth around it. The drift method finds evidences of alternating rainy and dry seasons, the death of animals on a building plain, and tar-seeps or springs for capturing the drifting bones and other debris in flood-time. Since evidences indicating the drift method of deposit have been confirmed during the years following the early discoveries, this method may well be set forth in a more extended sketch.