ON THE EREATICS IN THE BOULDER-CLAY OF CHESHIRE. 591 



44. On some Erratics in the Boulder-clay of Cheshire, Sfc.^ and 

 the Conditions of Climate they denote. By Charles Kicketts, 

 M.D., r.G.S. (Read May 27, 1885.) 



[Abridged.] 



The glacial phenomena in the valley of the Mersey indicate that, 

 though during that period the country was entirely covered with ice 

 and snow, these accumulations were no greater than were derived 

 from the snowfall on the water-slopes of this and its tributary 

 valleys. The glacier- strise on the surface of the Triassic rocks 

 coincide in direction with those of the respective vaUeys, or they 

 have a direct reference to the contour of the ground. Taking 

 " Happy Valley " (now Borough E,oad), Birkenhead, as a typical 

 example, the bottoms of the valleys, where channels have been in 

 pre-Glacial times, are filled to a limited height with irregularly 

 stratified beds of sand and gravel, their presence in other valleys 

 being revealed by excavations and borings for wells, &c. * The 

 sands have been derived from disintegration of the Trias ; whilst 

 the pebbles are similar to the erratics so abundant in the Boulder- 

 clay, excepting that all traces of striae &c. have been removed, it 

 is presumed, by water which, holding sand in suspension, issued 

 from beneath glaciers. On these gravels &c. is situated Boalder- 

 clay containing a much larger proportion of sand and pebbles than 

 the Boulder-clay proper. The flanks of the valleys frequently 

 have rock-surfaces covered with unstratified sands and angular 

 fragments of sandstone, without intermixture of erratic pebbles ; 

 they are considered to be moraine accumulations left by glaciers 

 which extended into the sea. The whole is covered with Boulder- 

 clay, a reddish-brown unstratified clay containing pebbles and 

 boulders irregularly dispersed through it. 



Besides the accumulations of Triassic fragments already alluded to, 

 others occur at from 125 to 150 feet above ordnance datum, which 

 must have been formed above the then sea-level, and have resulted 

 from the action of strictly local glaciers ; one was uncovered a few 

 years ago at the Birkenhead School, and another occurs near the 

 cemetery. 



The clay of the Boulder-clay may be attributed to the abrasion 

 of adjacent rocks by glaciers, beneath which it issued in subglacier 

 rivers highly charged with mud and sand. Such a condition occurs 

 in Greenland, where the rocks are of granite or of equally in- 

 destructible material f ; the quantity of sediment must therefore be 

 immensely increased when the strata passed over are so easily 

 disintegrated as the Trias and Coal-measures. The water being 



* " Buried VaUey of the Mersey," by T. Mallard Eeade, C.E., F.G.S. (Proc. 

 Liverpool Geol. Soe. 1872-73, p. 42). 



t " Physics of Arctic Ice," by Dr. Eobert Brown, F.R.G.S. (Quart. Journ. 

 Geol. Soc. vol. xxvi. p. 682). 



Q.J.G.S. No. 164. 2t 



