I had seen enough to convince me that they form a continuous convex stratum in the sandstone spear-shaft, covering it saddle-wise from side to side, dipping towards the Moray Frith on the south, and to the Cromarty Frith on the north--that, as in a _bona fide_ spear-shaft, the annual ring or layer of growth of one season is overlaid by the annual rings of succeeding seasons, and underlaid by those of preceding ones; so this huge semi-ring of fossiliferous clays and limestones had its underlying semi-ring of Red Sandstone, and its overlying semi-rings of yellow, of red, and of gray sandstone. I knew, besides, that beneath there was a semi-ring of conglomerate, the base of the system; and that, for more than two hundred yards upwards, ring followed ring in unbroken succession--now sandstone, now limestone, now stratified clay. But though intimately acquainted with these lower rocks for more than a hundred fathoms from their base upwards, and with the upper rocks on both sides the ichthyolitic bed for more than a hundred feet, there was an intervening hiatus, whose extent at this period I found it impossible to ascertain. And hence my uncertainty regarding the place of the ichthyolites, seeing that whole formations might be represented by the occurring gap. On the Moray Frith side, where the sections are of huge extent, a doubtful repeat in the strata at one point of junction, and an abrupt fault at another, cuts off the upper series of beds to which the organisms belong, from the lower to which the great conglomerate belongs. On the Cromarty Frith side the sections are mere detached patches, obscured at every point by diluvium and soil; and, in conceiving of the whole as a continuous line, with the Lias a-top and the granite group at the bottom, I was ever reminded of those coast-lines of the ancient geographers, where a few uncertain dots, a few deeper markings, and here and there a blank space or two, showed the blended results of conjecture and discovery--whether they give a _Terra Incognita Australia_ to the one hemisphere, or a North-Western passage to the other. The ichthyolites in a section so doubtful might be regarded as belonging to either the Old or the New Red Sandstone--to the Coal Measures, or to the Mountain Limestone. All was uncertainty.