• [The Rennie Shale] is only 50 to 75 feet thick and consists of soft olive argillaceous shale, sometimes micaceous...[limestone] nodules consist of an odd mixture of brown and blue limestone. Both sorts occur as distinct masses, sometimes sharply angular, but more frequently irregular in shape, and the change from one to the other is abrupt. The brown limestone, which looks like a fine sandstone is evidently rather pure calcium carbonate, judging from its rapid effervescence, and, since this portion of the rock does not scratch steel, it is assumed to be free of silica or sand. On the other hand, the blue limestone masses contain sand grains or silica, even though they also effervesce freely. Fossils are absent from the brown masses but are very abundant in the blue portions. Strangely, there are but two species of trilobites in these nodules...neither species has been recognized in the larger shale fauna."