584' Geological Sociciy: — Mr. Ljell on ihc 



rounded by ridges of detritus from fifty to seventy feet high, con- 

 sisting in the lower part of till and boulders, and in the upper of 

 stratified gravel, sand, loam and clay, in some instances curved or 

 contorted. The form of the included spaces is sometimes oval, 

 sometimes quadrangular. The finest examples are in the lower 

 tract, M'hich has the Dean for its southern boundary, and tlie road 

 from the bridge of lluthven to the south of the grounds of Lindertis 

 for its northern. The Grampian boulders are throughout the same ; 

 but there are associated with them masses of actinolite schist, which 

 Mr. Rlackadder has ascertained could be derived only from the val- 

 ley of (he 'lay. The fragments of secondary rocks belong to the 

 formations of the districts in which they occur. Though the country 

 occupied by these marl-loch lakes is not traversed longitudinally by 

 any river, yet it is so low, that if the transported matter were re- 

 moved, a very slight depression would cause the sea to flow from 

 Lunan Bay by Forfar to Blairgowrie and Dunkeld. Mr. Lyell 

 therefore formerly conceived that an estuary might have extended 

 in that direction, and that the till might have been drifted by 

 masses of ice floated from the Grampians and contiguous hills. The 

 overlying ridges of sand and gravel he thought might have been 

 bars formed one after the other, in the same manner as the bar of 

 sand and shingle, \vhich now crosses the mouth of the Tay. The 

 inland ridges of sand with boulders, which Mr. Lyell noticed in 

 Sweden, and certainly produced under the sea, confirmed him in 

 this view. These Swedish ridges are from fifty to several hundred 

 yai"ds broad, but sometimes so narrow on the top as to leave little 

 more than room for a road ; they are from fifty to a hundred feet 

 high, and they may be often traced in unbroken lines for many 

 leagues, ranging north and south. In his account of these ridges, 

 in a memoir published in the Philosophical Transactions*, Mr. 

 Lyell states his belief that they were thrown down at the bottom of 

 the Gulf of Bothnia, in lines parallel to the ancient coast, and during 

 the successive rise of the land. They usually consist of stratified 

 sand and gravel, the layers being often at high inclinations ; but 

 where they are composed of boulders, no stratification is observable. 

 After a long search, Mr. Lyell succeeded in finding shells in a layer 

 of marl belonging to a ridge in the suburbs of Upsala, about twelve 

 feet below the summit of the ridge, and eighty above the sea. The 

 shells consisted of Mytihts ednlis, Cardium edule, TelUna Baltica, 

 Litturina liiiorea, and Tvrbo nlva, the most common species in the 

 Baltic, and they constituted the greater part of the layer. On the 

 summit of the ridge, at a short distance, he noticed angular masses 

 of gneiss and granite, from nine to sixteen feet long, which had 

 evidently been lodged when the ridge was submarine. 



In Forfarshire Mr. Lyell never succeeded, as in the above case in 

 Sweden, in finding marine shells in the ridges of sand ; nor does he 

 remember to have seen in Sweden transverse ridges at right angles 

 to the north and south. The glacier theory, the author states, 



• 183o, pp. 15, IG. 



