Correspondence — Mr. W. T. Aveline, 527 



small stones than the Upper Clay. No large boulders were ob- 

 served ; but as the Lower Boulder-clay is not exhibited to any con- 

 siderable depth, it may possibly contain some such boulders. 



" The Middle Sands and Gravels consist of sands which frequently 

 by the great increase of rounded pebbles become gravels exactly 

 resembling those at Preston Junction and Wigan in Lancashire, and 

 Gresford, Corwen, and Colwyn in North Wales. 



" The Upper Boulder-clay contains comparatively few small stones, 

 but many large boulders, two or three feet in diameter. Many of 

 these are striated, and are composed of a dark greenstone; but some 

 are Criffel and Eskdale granite. These large boulders probably 

 occur at an average distance of twenty yards from each other. A 

 mass of compact gypsum about 4 ft. in diameter was also observed. 



"The excavators always worked the Upper Clay with a spade, and 

 the Lower Clay with a pick, in consequence of which the difference 

 between the two clays could be distinguished at a considerable dis- 

 tance, whether the Middle Sands and Gravels were between them 

 or not." 



I may now add that for many months during the progress of the 

 excavation the section was of the clearest possible character. Over 

 an area of many acres, the Upper Boulder-clay had been removed, 

 as well as the underlying Sands and Gravels, leaving the Lower 

 Boulder-clay untouched except where it rose above the general 

 level intended for the bottom of the Docks. In such instances it was 

 directly covered with the Upper Boulder-clay — though the line of 

 separation was invariably clear and distinct. The Middle Sands and 

 Gravels varied continuously, from fine and coarse sand into gravel 

 and pebble beds : and indicate very different conditions of deposition 

 compared to that of the two Boulder-clays. In conclusion I need 

 only remark that this tripartite division of Glacial deposits at Liver- 

 pool strengthens similar conclusions in North Wales and Lancashire, 

 and proves their general application over a wide area. 



122, London Eoad, Liverpool. George H. Morton. 



THE GRAPTOLITIC MUDSTONES OF THE LAKE DISTRICT. 



Sir, — Mr. C. Lapworth's argument in favour of the Graptolitic 

 Mudstones of the Lake district being Lower Llandovery would be 

 very strong if there was a physical break between them and the 

 overlying formations, but this is not the case. The Mudstones gra- 

 duate upwards into the pale and purple-coloured slates, which in their 

 turn graduate upwards into the Coniston Flags, and so upwards into 

 the Bannerdale beds. From the base of the Mudstones to the top of 

 the Bannerdales is one conformable series. The disappearance of the 

 Graptolites of the Mudstones is not sudden, they are found in the 

 dark bands interstratified with the pale slates to the very top. 



I do not believe there can be an enormous break indicatino- a lone: 

 lapse of time without there being some signs of unconformity or 

 overlap ; in this case there is none, not even a sharp junction. 



Kendal, 20th Oct., 1876. W. Talbot Aveline. 



