160 PROCEEDINGS OF THE 



In tlie absence of recognisable characters for determining the 

 nature of these objects, I had recourse to the microscope, and com- 

 pared the tissue with that of many pLants, terrestrial and aquatic, 

 but generally selecting root fibres. I was led, as a result of these 

 examinations, to regard them as fibres of the rhizome of some 

 species of Equisetum, the elongated cells being well marked, and of 

 the usual brownish colour. Similar vegetable tissue — sometimes in 

 a comminuted state — was revealed on an examination of clay from 

 West-thorn, from Paisley, and from a cutting at the head of 

 Eglinton Street. 



There is nothing in the geological history of the sandy clay in which 

 these roots are found to militate against their equisetal origin ; on 

 the contrary, such an idea is confirmatory of the supposed conditions 

 under which this stratum was formed. It marks the last day of 

 a glacial epoch, when the land was slowly rising, and although the 

 clay beneath is clearly shown to have been of marine origin, from 

 the discovery of a few species of shells, we have no data to indi- 

 cate a similar origin for this upper deposit. It must be remem- 

 bered, too, that the plants themselves existed only very near to 

 the surface of the bed, where the waters would be only shghtly, if 

 at all brackish, and forming extensive shallow marshes. There is 

 abundant evidence that considerable denudation followed the com- 

 pletion of those strata, and this would account for the disappear- 

 ance of the stems of the Eqnisetm, while the roots beneath 

 remained. 



How long this process of denudation continued, caused, as it 

 probably was, by considerable alterations of level, no one can tell. 

 Consequent on it, however, the Clyde seems to have assumed its 

 present course, flowing in a much wider channel, and much more 

 rapidly, than now. The coarse gravel wliich rej^resents this period! 

 contains nothing of botanical interest beyond a few decayec 

 branches, wliich lie here and there throughout its extent. The] 

 land would as yet be naked and bare, but slowly preparing for] 

 that abundant vegetation Avhich we find in the later strata.! 

 Animal life is represented solely by the fresh water mussel, Unio 

 margariiifera, the epidermis of which was first discovered byj 

 Mr Bennie, and he has, in a limited area of Windmillcroft, found | 

 seventy of these skins, thus indicating a notable al)undance of the 

 species. In many instances a sandy cast in the gravel showed 

 where the mollusc had lived and died — the position of the 



