1862.] HAEKNESS PTERASPIS-BEDS. 257 



glomerates made up of quartz-pebbles, wbich at this spot have 

 almost a vertical position. The conglomeratic portion of this series 

 becomes more prevalent in the lower members, and finally we have 

 a very great thickness of these latter exclusively occurring. The 

 fragments which enter into the composition of these last conglo- 

 merates differ from those in the higher beds of the Old Eed Sand- 

 stones of the Keltic; for in these lowest conglomerates rounded 

 fragments of felstone almost solely make up this portion of the series ; 

 and these fragments vary very greatly in size, some being as much 

 as two feet in diameter. The lower conglomerates, which are devoid 

 of any trace of stratification, are well seen in the Keltic immediately 

 opposite the small farm-house on the east side of the stream. Above 

 these conglomerates, which are nearly a thousand feet in thickness, 

 we come upon a fine exhibition of trap -rocks occupying the line of 

 fault which separates the Old Red Sandstones on the S.E. from the 

 metamorphic rocks of the Grampians on the N.W. 



The sequence of deposits, as represented in the course of the 

 Keltic, has a great affinity to that which occurs on the southern 

 margin of the Old Eed Sandstone of Scotland north of the Forth 

 and Clyde, as seen in the neighbourhood of the Bridge of Allan and 

 in the course of the Teith. In the former locality we have, how- 

 ever, a much greater development of the conglomerate series which 

 forms the lowest member in both these areas ; and in both instances 

 we have these conglomerates succeeded by grey sandstones, the latter 

 at the Bridge of Allan affording Cephalaspidian remains. In the 

 course of the Keltic the grey sandstones are succeeded by purple 

 beds ; and the like circumstance marks the superposed beds on the 

 grey sandstones north of the Bridge of Allan. Upon these we have 

 the purple shales of Leckrop, which in the Keltie section are repre- 

 sented by thin-bedded, light-purple, micaceous sandstones; and 

 upon these there are found brown sandstones and conglomerates 

 which are the equivalents of the brown sandstones of the Ardoch, 

 of Doune, and of Lanrick. In the Keltie and in the Teith this por- 

 tion of the series has reposing upon it the grey flaggy strata which, 

 in the section between the Bridge of Allan and Callander, form the 

 highest beds of the Old Red Sandstones in this part of Scotland. 



With reference to the thickness of the strata exhibited in the 

 Keltie, — if we take the distance from the trap-rocks which inter- 

 vene between the metamorphic Lower Silurian rocks on the N'.'W. 

 and the spot where, in this stream, the upper grey beds become 

 horizontal, as two miles, measured along the dip, and the average 

 angle of dip as 45° (which is most probably below the mean), then 

 we have, in the course of the Keltie, from the lowest beds of the 

 conglomerate to the highest beds of the upper grey sandstone series, 

 a thickness of more than 7000 feet of strata appertaining to the 

 Old Red Sandstone m South Perthshire. In the arrangement of the 

 mineral matter which forms these Old Red Sandstones we have a 

 much greater affinity to the deposits which represent this series in 

 the N.E. of Scotland, than to those of the extension of the Perth- 

 shire deposits as they occur north-eastward in Forfarshire and 



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