188 PROCEEDnfGS OF THE GEOLOGICAL SOCIETT. [Jan. 11, 



§ 6. Seco>"d Peeiod of Depeessio^'. 



a. Old Estuarine Beds and Beaclics. — After the period represented 

 by the forest-bed just described Tve have evidence of a depression of 

 the coast, which seems to have been very general along the shores 

 of this country. In the Firths of Tay and Forth this depression 

 caused the sea to reach about 2b or 30 feet above the present coast- 

 line, so as to cover the rich flat country of the Carses, as they are 

 locally termed. These Carse-lands are plains of fine silty clay, quite 

 free from stones, and identical m character with the sediment now 

 forming along the shallows of the present estuaiies. It forms a 

 smooth level sheet of rich mud occupying the whole width of each 

 valley, and encircling the little rocky eminences and mounds of old 

 glacial de'bris that project through it, much iu the same way as the 

 waters of a lake do the islands on its surface. In the district of the 

 Tay it forms the Carse of Gowrie, the garden of Scotland, together 

 with the flat lauds at the mouth of the Earn. A narrow strip of it 

 extends even a little above Perth, towards Scone, forming the rich 

 ground of the Muii'town farms. 



The Carse of the Forth, however, is the most extensive tract of 

 this natui-e in Scotland. It stretches for many miles inland, over- 

 lapping the eastern base of the moraine-hillocks of the Loch of ilon- 

 teith, and extending through a narrow opening up to Gartmore ; 

 while below StirUng it forms a broad margin on the south side of 

 the valley down to Grangemouth, and on the north side to Alloa. 

 Mr. Blackadder gave a good account of it many years ago in the 

 fifth volume of the "Wernerian Society's Memoirs, with a map show- 

 ing its boundaries. A fine view of this beautiful plain is got from 

 Stirhng Castle. Marine shells of the kinds generally found in 

 estuaries occur in some places abundantly. 



For example, on the banks of the Forth, near Micklewood, some 

 five miles to the west of Stirling, there are seams of shells imbedded 

 in the old estuarine mud up to a height of 6. feet above the surface 

 of the river ; and as the tide is not now felt so far up the Forth, the 

 elevation above the sea must be a little more. The species I found 

 here were : — 



Cardhnn edulc. Abundant ; generally of small size. 



Mi/tUus edulis. Common. 



Osfrea edulis. Frequent ; mauy of the shells are very thick. 



Tellina soliduJa. Occasional. 



JSa'obicularia jpqyemta. Xot very numerous. 



Hissoa idv(v. Frequent. 



Littorina litorea. Pare. 



Fu^us antiquKS. One broken specimen. 

 The most abundant of these by far Avas the Cockle ( Cardium), the clay 

 being in some places quite crowded with their remains. The size is 

 small, as if they were yoxmg shells ; mauy of them are quite entire, 

 but the generality are decayed and broken. These shells occur in 

 an xmdulating seam, which sometimes passes underneath the surface 

 of the water, and at others rises a few feet above it. Occasionally 

 there are two seams. 



