THE OLD RED SANDSTONE.

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rocks for more than a hundred fathoms from their base up-wards, and with the upper rocks on both sides the iclithyolitebed for more than a hundred feet, there was an interveninghiatus whose extent at this period I found it impossible toascertain. And hence my uncertainty regarding the place ofthe ichthyolites, seeing that whole formations might be re-presented by the occurring gap. On the Moray Frith side,where the sections are of huge extent, a doubtful repeat inthe strata at one point of junction, and an abrupt fault atanother, cuts off the upper series of beds, to which the or-ganisms belong, from the lower, to which the great conglome-rate belongs. On the Cromarty Frith side the sections aremere detached patches, obscured at every point by diluviumand soil; and, in conceiving of the whole as a continuousline, with the Lias atop and the granite group at the bottom,I was ever reminded of those coast-lines of the ancient geo-graphers where a few uncertain dots, a few deeper markings,and here and there a blank space or two, showed the blendedresults of conjecture and discovery,—whether they give aTerra incognita Australia to the one hemisphere, or a North-Western passage to the other. The ichthyolites in a sectionso doubtful might be regarded as belonging to either the Oldor the New Red Sandstone,—to the Coal Measures or to theMountain Limestone. All was uncertainty.

One remark in the passing : it may teach the young geo-logist to be cautious in his inferences, and illustrate, besides,those gaps which occur in the geological scale. I had nowdiscovered the ichtliyolite beds in five different localities. Inone of these,—the first discovered,—there is no overlyingstratum;—it seems as if the bed formed the top of the forma-tion : in all the others the overlying stratum is different, andbelongs to distant and widely-separated ages. We cut in onelocality through a peat-moss,—part of the ruins, perhaps, of