344 



The Scottish Naturalist. 



Highland valleys, and discharged large volumes of muddy water 

 during summer. 



"4th. Elevation of the land now ensued, and the sea retreated to 

 lower and lower levels, until eventually the coast extended 

 farther into the North Sea than is now the case. (Probably this 

 stage was synchronous with the re-appearance of a vigorous forest- 

 growth in the lower reaches of our great estuaries). 



"5th. The sea again advanced, and cutback into the Montrose 

 Basin, upon the margin of which we now find bluffs formed of the 

 old Scrobicularia-silt and the overlying estuarine or brackish- 

 water carse clay." 



In connection with the last paragraph it may be remarked that 

 we have no evidence of a sea bottom over the carse clay, and if it 

 was deposited after a secondary glacial period, the South Esk 

 itself may have worn the present Basin out of the carse clay and 

 old estuary silt, when the general level of the land differed little 

 from the present one. 



However this may have been, it is worthy of note that the 

 molluscs now living in the Backsands are identical with those 

 found in the old estuary beds, and it seems probable that the 

 Scrobicularia and its congeners are the direct lineal descendants 

 of the old estuary silt, just as our modern peat plants are probably 

 descended from those much more extensive bogs in which they 

 nourished at the end of the great ice age. That climatal or 

 other conditions have changed, and are still changing, is evinced 

 by the fact that many of the molluscs of the old silt have become 

 extinct, while others which yet survive are evidently playing a 

 losing game in the struggle for existence. The oyster, once 

 abundant in the estuary, is, alas ! represented now only by dead 

 shells. Cylichna cylindrica, Kellia suborbicularis and others have 

 gone with the oyster, while Lutraria elliptica, and Scrobicularia, 

 the mud monarch of the olden times, have dwindled to small 

 colonies on the Rossie side of the Basin. 



The zoology of the present Basin estuary is, however, still full of 

 interest. Annelides, some zoophytes, a few Crustacea, including 

 the curious Corophium longicorne, and over forty species of 

 mollusca are to be found alive in it. These in their turn attract 

 many wading and swimming birds, some of them rare visitors to 

 our coasts. The botanist will also be interested to find, besides 

 some algae, Zostera marina in abundance on the mud banks at low 

 water. 



