22 MONOGRAPH OF DURA DEN. 



rivers Esks, the Isla, the Ericht, the Brand, the Taj, the Earn, 

 and other mountain-streams that leap from Glcn-Artney and 

 precipitous passes to the westward. Good sections of this 

 formation have been exposed on the Dunkeld hne of railway, 

 under Birnam hill ; the ma,in drive of the newly-formed 

 aqueduct from Loch Vennachar to Glasgow intersects the 

 conglomerate, where it is elevated in many places into lofty 

 ridges of several hundred feet in height ; and, at intervals, it 

 is traceable along the shores of the Clyde, and largely developed 

 in the islands of Bute, the Cumbrays, and Arran. 



A series of grey sandstones of great thickness succeed the 

 conglomerate, resting unconformably upon its more inclined 

 edges {gh). These correspond in age and position with the 

 Caithness fossiliferous flagstones, while several of the beds are 

 wanting, especially those so rich in the coccosteus, palseoniscus, 

 and cheirolepis families. They range over the Mearns, Strath- 

 more, and Forfarshire ; occupy the central and upper districts 

 of Strathearn from Comrie to Doune ; and, easterly, traverse 

 the Carse of Gowrie and estuary of the Tay to Dundee and 

 Arbroath. The celebrated fossiliferous deposits of Balruddery, 

 Carmylie, Tealing, Craig, and Parkhill are all embraced within 

 the area now traced of these grey sandstones, some of which 

 are extremely fissile and flaggy in their beds, and others more 

 gritty and micaceous in their characters. 



The strata all dip off" from the Grampians, generally in a 

 south-easterly direction, and at various degrees of inclination. 

 The thickness of the group may be estimated at about 2000 

 feet. The deepest section is exposed in the quarries of Bal- 

 beuchlie ; and the beds, uptilted at various angles, proceed 

 along the ridges and numerous valleys of the highest crest 

 of the Sidlaws. There are in the line of strike from north to 

 south, two well-defined synclines and three anticlines, occa- 

 sioned by the upheaval of the trappean formations. 



The suite of sandstones under consideration are extremely 

 rich in organic remains, consisting of cephalaspis, pterogotus, 



