On the Position of the Pteraspis Beds, and on the Sequence of the Strata of the Old Red Sandstone Series of South Perthshire

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Introduction —In the ‘Quarterly Journal of the Geological Society,’ vol. xvii. p. 541, Mr. Powrie mentions the occurrence, for the first time, of Pteraspis in the Old Red Sandstone of Scotland, as developed in the neighbourhood of the Bridge of Allan in Perthshire. The specimens obtained by this geologist I had an opportunity of seeing in his possession in the early part of this year. Being under the impression that this area was occupied by that portion of the Old Red Series which is so extensively developed in Fife and Kinross, and which appertains to the upper portion of the series, it occurred to me that either there was something anomalous in the position of these Pteraspidian remains, or that the true horizon of the strata in this portion of the southern margin of the Old Red Sandstone north of the Firths of Forth and Clyde had yet to be determined. Under this impression, I was induced to examine the district around the Bridge of Allan; and I was also induced to extend my observations north-westward, across the Old Red Sandstone area of this part of Scotland, to the metamorphic rocks of the southern margin of the Grampians, as these occur N.E. of Callander. The result of this has been to ascertain the position of the Pteraspis-beds, and likewise to show a variation in this section from the lithology which usually obtains in the deposits which make up the Old Red Sandstone areas lying to the N.E. of the line of

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