The Sonora Journal gives an account of a very singular ledge of rocks which has recently been discovered in Petaluma in California. It is composed of regular prismatic columns, inclined but a few degrees from the perpendicular toward the center of the hill. The columns generally have five sides, and are usually about twenty inches in thickness, divided into two blocks varying from one to four feet in length, which are so closely jointed and so firmly cemented together that it is quite difficult to separate them. The columns are also bound to each other by a layer of grayish colored cement, about an inch in thickness. The rock is very hard, and of a dark color, and belongs to that class of rocks denominated basalt by geologists. The whole ledge presents the appearance of a solid structure of masonry, reared, like the Egyptian Pyramids, to perpetuate the works and memory of man, in defiance of the flight of ages. So abundant, indeed, are the appearances of design, that we are not surprised that many persons have unhesitatingly pronounced it the work of art. There is abundant evidence, however, that precludes the possibility of such being the case. This columnar structure of rock is not unfrequent. It is seen along the margin of Snake River, and in the passage of the Columbia River through the Cascade Mountains, perpendicular walls of this columnar structure are often seen rising to the hight of forty or fifty feet. The rocks are easily quarried and brought to town, but the greatest advantage of all is their thorough adaptability to the construction of fire-proof buildingsneither fire or water affecting them in the least. We saw a chip from one of the rocks subjected to fire until it became heated to a bright red color, after which it was immediately thrown into cold water. No change whatever from its original appearance could be perceived.