These blocks are beautiful, and way cool, and with excellent graphics on the box, too. I have done a good bit of searching but can only find one mention of them out there: there are a few boxes of these held in the collection of the National Building Museum in Washington, DC Boxes, though with no more information about them than I've got.  The museum describes them as stone, which is what they seem to me to be (as if the lynchpin between antique stone Anchor Blocks and interlocking plastic Lego)--but, oddly, they were produced by "Miniature Plastics, Inc.) of Newark, NJ, so perhaps the material is some sort of stone-like composite. I found three boxes together--one filled, two full layers deep, with brick red blocks; the second also full, two layers deep, with mostly gray ones (with some great variations in color, as shown), and a third with some more blocks plus paper roofs and windows and doors.

I didn't give myself time to dive deep into playing/building with them, but there are enough blocks here to construct all sorts of elaborate things, and the blocks interlock beautifully, with plenty of single pronged ones in addition to the doubles. A rare find for the building blocks collector (or builder, or architect, or designer, or bricklayer!) but also great for the kids--and, as described on the side of the box, "designed especially to develop creative ability in children of all ages."  Great.

Box measures 7 1/2" x 4 1/4" x 1 1/8". Two layers deep of bricks stacked sideways in two of the boxes; some bricks plus paper roofs, doors, windows, etc. in the third. All in excellent condition.