D. MACKINTOSH ON HIGH-LEVEL MARINE DRIFTS. 



351 



26. Oil the precise Mode of Accumulation and Derivation of tlu 

 Moel-Tryfan Shelly Deposits ; on the Discovery of Similar 

 High-level Deposits along the Eastern Slopes of the "Welsh 

 Mountains; and on the Existence of Drift-zones, showing 

 probable Variations in the Rite of Submergence. By D. 

 Mackintosh, Esq., F.G.S. (Read April 27, 1881.) 



Contents. 



I. Introductory Remarks on the variable Character of the Lower Boulder- 

 drift of the Lake District, North Wales, &c. 

 II. Moel-Tryfan Deposits, &c. 



III. Deposits on Halkin Mountain, Flintshire. 



IV. Discovery of High-level Deposits of Gravel and Sand between Minora 



and Llangollen Vale, Denbighshire. 

 V. High-level Gravel and Sand near Llangollen. 

 VI. Eemarks on the High-level Gravel and Sand of Macclesfield Forest. 

 VII. Arrangement of the Drift-deposits of North Wales into Vertical Zones, 



showing probable Variations in the Eate of Submergence. 

 VIII. Concluding Remarks as to whether the Submergence was caused by 

 Subsidence of the Land or Rising of the Sea. 



I. Introductory Remarks on the variable Character of the 

 Lower Boulder Drift of the Lake District, North Wales, &c. 



Many years' observations along the east coast of the Irish Sea, from the 

 Solway Frith southwards to the estuary of the Dee, have led me to con- 

 clude (as stated in former papers published in this Journal) that while 

 the Upper Boulder-clay is a remarkably persistent and homogeneous 

 formation, and while the line of separation between it and the 

 cleanly washed, obliquely laminated, and boulderless sand and gravel 

 (where the two formations are present) is always distinctly marked, 

 the Lower Boulder formation varies both vertically and horizontally 

 from compact stony clay to loam, gravel, and sand. This is more 

 especially the case in the neighbourhood of the mountains and at 

 comparatively high levels. Around the mountains of the Lake 

 District (where it is called pinnel) it is often interstratified with or 

 replaced by well-laminated and often contorted sand and gravel, as 

 at Ulverston Railway station, between Ulverston and Arrad Foot, 

 <fcc. In the neighbourhood of Bangor, though a stiff Boulder- clay 

 may here and there be seen lying under stratified sand and gravel, 

 the two kinds of drift may quite as often be found in horizontal 

 succession ; and they both agree in containing boulders (see VII. 

 1 and 2). 



II. Moel-Tryfan Deposits, &c. 



1. Brief History of Discovery. — In 1871, and again in 1880 (last 

 year), I had opportunities of tracing the drift-deposits of Caernar- 

 vonshire from the neighbourhood of Bangor to the top of Moel 

 Tryfan, and of observing a number of facts connected with the Moel- 



