340 report — 1879. 



instances the whole surface is eroded, causing organisms to project in relief: more 

 frequently a considerable area is affected whilst the remainder continues ice- 

 scratched and intact ; often hollows or channels have been formed, the other portions 

 retaining the ice-marked surface. In some instances of impure limestone the car- 

 bonate of lime has been dissolved away in parts, leaving behind the insoluble sand 

 or mud. A few blocks of carboniferous limestone not only bear marks of glacial 

 erosion, but are covered with borings fonned by marine animals ; one example is 

 likewise chemically eroded in channels. 



Even some hard quartzites have not escaped weathering, as indicated by con- 

 cealed joints and by channels hollowed on their surface. 



Single fragments of glaciated pebbles of Silurian grits and slates are often found 

 detached ; a very few have the separate pieces lying at a short distance from each 

 otter: but in many, though quite separate, they are exactly in apposition, the 

 pebble itself being broken into two or many parts. 



From the examination of these different examples of glaciated and weathered 

 pebbles, it may be inferred that they had formed portions of moraines on land, and, 

 as a consequence of being there exposed repeatedly to successions of frost and thaw, 

 have become thus weathered and split into fragments ; those blocks of limestone 

 which have been perforated by marine organisms bear evidence to their deposition, 

 for a period, in a moraine accumulation beneath the sea. Subsequent to this reces- 

 sion an increase of snow-fall has caused an extension of the glaciers, which in its 

 progress carried forward the accumulation into the sea, either directly, or by joining 

 a main glacier from which the bergs have been broken off that conveyed away these 

 boulders. As these erratics are common in the Boulder-clay at different horizons, 

 it follows that there must repeatedly during a prolonged period have been a 

 succession of instances of an advance and retreat of glaciers similar to what is 

 recorded as taking place in Greenland. 1 



When examining moraine accumulations, pebbles of carboniferous limestone 

 were obtained which were glaciated, weathered, and fractured, in a similar manner 

 to some from the Boulder-clay ; also similar fractured pebbles of Silurian grit and 

 of Longmynd rock have been met with under the same conditions. 



The existence of these pebbles both in moraines and also in the Boulder-clay 

 illustrates what had been deduced from previous investigations in the Valley of the 

 Mersey — that in Britain, during what is called the Glacial Period, ' the glaciers did 

 not progress from an immense accumulation in the north, but were formed by the 

 snow-fall in the respective valleys ; being of such an extent only as might reason- 

 ably be considered due to the amount of deposition on their water-slopes.' 2 



6. On the Volcanic Products of the Deep Sea of the Central Pacific, with 

 Reference to the ' Challenger ' Expedition. By the Abbe A. Renard and 

 T. Murray. 



The mineralogical and penological researches on the sea-bottom of the Pacific 

 area extending from the Sandwich Islands to the 30th degree of S. latitude, and 

 having the Low Archipelago in its approximate centre, show that volcanic matter 

 plays an important part there. It i3 present in the form of lapilli and of ashes 

 spread in great abundance in the ' red clay.' These lapilli nearly all belong to the 

 basaltic type, passing from the felspathic basalts to allied rocks in which the 

 vitreous base assumes greater and greater development until it almost completely 

 displaces the crystalline constituents of basalt. The fragments then become true 

 glassy rocks of the basic series, in which are still found generally crystals of 

 peridote, and numberless crystallites which are sometimes grouped in opaque 

 granules or arranged regularly around the niicrolites of peridote. The forms of 



1 ' On the Fiords, &c. of Norway and Greenland,' by Amund Helland, Fellow of 

 the University of Christiana. — Quart. Journ. Geol. Soc. vol. xxxiii. page 142." 



2 ' The Conditions existing during the Glacial Period,' &c, by Charles Ricketts. 

 — Proc. Liverpool Geol. Soc, 1876-77. 



