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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 19, 



up over the whole district. Parexus incurvus is founded, by Agassiz, 

 on a very striking spine from Balruddery, but has also been detected 

 by me at Canterland, the other extremity of the district. Parka de- 

 cipiens, occasionally with an attached ligament or stem, or even with 

 what resembles a calyx or sheath, is universal, and abundant in 

 every section and in every quarry. Pterygotus is almost as widely 

 dispersed, though generally in a fragmentary condition ; and for it the 

 same localities may be stated as for Gephalaspis, with the exception 

 of Brechin, but substituting in place thereof Famell, where plates of 

 the larger Crustaceans and complete forms of the smaller have been 

 found by the author and Mr. Powrie of Beswallie. Kampecaris was 

 described by Page from Balruddery, and has been found (perhaps 

 several species) by me at Canterland, the extreme of the area. Some 

 of the vegetable forms are generally diffused, bike Parka decipiens, 

 occurring in every opening of the fossiliferous beds. Indeed the only 

 form, with the exception of the Crustacea (which are yet undescribed), 

 confined to one locality is CUmatius reticidatus, recorded by Agassiz 

 from Balruddery ; but the genus is founded on a spine, and in the 

 multitude of our spines it might be easily passed over. 



§ 8. Distribution of the Fossils through the vertical depth of the 

 Strata. — Though spread over a wide area, the arrangement of our 

 rocks is very simple. In the section at Canterland (which is typical 

 of the district) we have, first and lowest a gritty sandstone* (120 feet 

 seen), very ferruginous, and containing occasional thin layers of a 

 purplish flag ; secondly, grey flagstone with intercalated sandstones 

 (40 feet)f ; and thirdly and above all, an overlying conglomerate j. A 

 similar life seems to have prevailed throughout the entire formation, 

 as embracing an era in geological time. We have met with a soli- 

 tary but well-preserved Parka decipiens § far beneath the fossilife- 

 rous grey beds in the gritty sandstone which forms the bottom-rock 

 in the Canterland section. The Gephalaspis is found occasionally in 

 the sandstones used for building-piu'poses, as at Brechin (imme- 

 diately below the grey flagstones), in which, owing to the nature of the 

 matrix, not another organism is known. But whilst this is all the 

 direct pakeontological evidence, there is other evidence of a physical 

 character. Among the purple flags, which he very low in the for- 

 mation, there have been gathered slabs containing on their surfaces 

 impressions, numerous and well marked, of what we may call the 

 phenomena of a sea-shore of this pala30zoic epoch. On that sea- 

 shore the tides must have ebbed and flowed, the rain have fallen, now 

 in heavy shower, anon in drizzling mist, the sun must at times have 

 shone with sultry beam, and many creatures have travelled across 

 the palimpsest surface. Besides the AnneHde-markings, we have 



* Judging from the di^D and the neighbouring rocks, this sandstone probably 

 rests on a dark-red sandstone. 



t In the quarries at Carmylie these are 120 feet thick. 



\ A few feet thick here, but several hundred feet thick as it rises up the neigh- 

 bouring hills. At the Hill of Turin, conglomerate (2 feet thick) is intercalated 

 amongst the grey flagstones. 



§ Sir K. I. Murchison and Mr. Powrie found the Parka decipiens common in 

 the lower conglomerates on the mountain or western flank of the basin. — Edit. 



