'30 D. MACKINTOSH ON SOME NEW SECTIONS 



39. On a number of new Sections around the Estuary of the Dee 

 which exhibit Phenomena having an important bearing on the 

 Origin of Boulder-clay and the sequence of Glacial Events. 

 By D. Mackintosh, Esq., F.G.S. (Bead June 20, 1877.) 



Contents. 

 Introductory Remarks. 

 Results of Additional Visits to the Dawpool Sea-coast Section. 



Line of Junction between the Lower and Upper Boulder-clays. 

 Deposits at the Base of the Lower Clay. 

 Character of the Striated Erratic Stones. 

 Signs of Boulders having been dropped. 

 Sections on the West Shore of the Estuary of the Mersey. 

 New Dock-sections near Bootle. 

 Sections around Birkenhead, showing the Relations between the Boulder-clays 



and the underlying Rock-surfaces. 

 Derivation of the Component Materials of the Boulder-clays. 

 Persistent Line of Demarcation between the Middle Sand and the Upper Clay. 

 Striated Rock-surfaces, and their Relation to the Direction in which Erratic 



Stones have been carried. 

 Horizontal and Vertical Range of the Two Boulder-clays of the Basin of the 



Irish Sea. 

 Horizontal and Vertical Range of the Middle Drift. 

 Is there any " true Till" at low levels in the Basin of the Irish Sea ? 



Introductory Remarks. — In his Survey l Memoir on the Geology 

 of North Wales,' p. 207, Professor Kamsaj" remarks " how necessary 

 it is to map every possible formation in detail before we can arrive 

 at just conclusions concerning either the completeness or the frag- 

 mentary nature of the succession of strata." It is only by keeping 

 a keen outlook in a particular district or districts for new sections 

 that such details can be obtained. As regards drift-deposits, sec- 

 tions are likely to vary so much with the extent of the excavations, 

 the state of the weather, &c, that, before they can furnish reliable 

 facts, it is necessary that they should be leisurely and repeatedly 

 observed. Though familiar with a number of sections around the 

 estuary of the Dee for many years, I have lately seen the necessity 

 for making a series of more connected and systematic observations 

 than time had previously permitted ; and as some of the sections 

 may soon become obliterated, I lose no time in communicating the 

 results to the Geological Society. 



Results of Additional Visits to the Dawpool Sea-coast Section. — 

 Since the time I very briefly described this section in the Quart. 

 Journ. Geol. Soc. for Nov. 1872* I have often visited it, and on 



* I must here correct two errors into which I was led during my earlier 

 visits to Dawpool (Quart. Journ. Geol. Soc. for Nov. 1872). The grey facings 

 of the fractures in the upper clay are not a chalk-wash, as was suggested to me 

 by an eminent geologist; and their nature and origin have not yet, I believe, 

 been satisfactorily explained. Though not at the points where I then examined 

 i lie Dawpool cliffs, the upper clay of Cheshire does contain much decomposing 

 "greenstone," as well as the lower. Both clays contain carbonate of lime, 

 which, if it did not come from the chalk of Ireland, may have been derived 

 from the limestone of Westmoreland, N.W. Lancashire, or W. Cumberland. 



