A CACHE OF BLADES continued for the long thin flakes and splinters into which it readily fractures. It was a good stone for spearheads or arrowheads, knives or drills, better than the common Potomac materials, the cobbles and pebbles of brittle white quartz or toughish gray and brown quartzite found along the stream beds. And so it seems to have been very much worth while to the Indians of the Potomac Valley, during some phase of their history at least, to quarry for rhyolite back in the mountains. Holmes reports that they distributed the stone thence throughout twenty thousand square miles of the "Potomac Chespeake 88 Province." An early United States Geological Survey furnished him with a map of outcroppings of this rock, as it occurs across Pennsylvania and Maryland in a range of the Appalachians. Holmes found chips in the roadway at Maria Furnace, on a branch of the Monocacy River (HI on the map), and he discovered that on the steep side of the mountain above the stream the quarry workings extended for several acres. He believed that other quarries existed somewhere in these mountains, but apparently no one has continued his explorations. Over the course of the years I have succeeded in col-