Geological Society. 517 



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, which 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 

 yards 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 Mytilus edulis, Cardium edule, Tellina Baltica, 

 Littorina littorea, and Turbo ulvce, 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, 

 appears to ofl!^er a happy solution of the problem of the marl-loch 

 gravels, the longitudinal banks being regarded as lateral and medial 

 moraines, and the transverse ridges as terminal. The chief objec- 

 tions are the stratification of the upper part of the banks, and the 

 necessity of assuming a glacier thirty-four miles in length, with a 

 fall of only 300 or 400 feet of country. 



It has always appeared to Mr. Lyell and Mr. Blackadder remark- 

 able, that the marl-loch gravels at Forfar are nearly 100 feet above 

 the tract of till which separates them from the valley of South Esk, 

 in Strathmore. In the present configuration of the country, water 

 could not deposit the Forfar gravels without extending to the South 

 Esk, the detritus of which is distinct, and separated by a low district 

 of till without gravel. The only explanations of these phsenomena 

 Mr. Lyell considers to be either that the till is the moraine of a 

 glacier, or that there has been a local change of relative levels of 



* 1835, pp. 1.5, IG. 



