592 



C. RICKETTS ON THE ERKATICS IN THE 



thus surcharged -with mud may account for the entire absence of 

 marine life ; fractured, rarely perfect, shells occur sparsely scattered 

 in the clay, but neyer under such circumstances that it could be 

 imagined they had lived where found. 



The pebbles and boulders imbedded in the clay, and from which 

 the formation derives its name, consist of fragments of hard rock 

 from the size of minute grains to two or three feet or more in 

 diameter, such as may have been derived from lands encompassing 

 the Bay of Liverpool and the adjoining portion of the Irish Sea — 

 from Cumberland, the south-west of Scotland, the north and east of 

 Ireland, and K'orth^^ ales. Their surfaces are very generally flattened, 

 smoothed, and polished, and a large proportion are covered with 

 striae, grooves, and scratches, universally acknowledged to have been 

 caused by abrasion beneath glaciers. If it is conceded that they 

 have dropped into the clay from floating ice, their number is such 

 as would indicate that the whole bay was sufiiciently packed with 

 bergs and floes to prevent altogether the formation of waves *, and 

 therefore, in the absence of other currents, no evidences of strati- 

 fication are afforded. 



Amongst the erratics in the Boulder-clay may be included masses 

 of unconsolidated sands and gravels, often alluded to by local 

 geologists as " pockets of sand," &c. The materials resemble accumu- 

 lations already referred to as situated in the bottoms of valleys as a 



bed upon which the Boulder-clay reposes ; their general shape is 

 comparable to that of the section representing masses containing a 

 remarkable collection of dark green blocks of disintegrated traps, 

 unmixed with other boulders, exposed in 1878 during the con- 

 struction of the Bootle Docks (fig. 1). These were imbedded in a 



Pig. 1. — Section in Bootle Docks, Liverpool. 

 (Length aboat 28 feet.) 



a. Trias. h. Gravel. c. Boulder-clay. 



d. Masses containing disintegrated Trap. 



light green sandy matrix, and formed accumulations which were 

 very conspicuous, the colour being in marked contrast to that of the 

 Boulder-clay ; their disintegration must have been due to the same 



* " However great the agitation of the sea may be in the open ocean, and 

 though it may dash its waves with wild fury on the edge of the ice, within the 

 ice-girdle it is undisturbed" ('New Lands within the Arctic Circle,' by Lieut. 

 Julius Payer : chap. i. § 23). 



In January 1881 the Mersey was covered with floating ice, or rather snow, 

 for nearly its whole width ; on the waves reaching the ice they terminated in a 

 swell for a short space, whilst inside the surface was perfectly unmoved. 



