QUATERNARY DEPOSITS OF BRITISH ISLES ^BROOKS. 337 



The section lies at a height of 800 feet in a small valley between 

 some outlying granite hills. The surface is now pasture. No. 1 

 was referred by Mr. Williams to the lower bowlder clay, but it' con- 

 tains a large number of limestone pebbles, and is, therefore, on the 

 horizon of the upper bowlder clay. (2) is simply rewashed bowl- 

 der clay. (3) contains so much vegetable matter that it can hardly 

 be called a clay. From the total absence of any tenacious clay like 

 (2), Mr. Williams infers a decrease of the rainfall. (4) is a la- 

 custrine clay containing a considerable jDroportion of vegetable mat- 

 ter, interstratified with seams of clay and fine quartz sand. Ac- 

 cording to Mr. Williams it indicates genial or temperate conditions 

 like the present. Numerous remains of Cervus nvegaceros^ chiefly 

 skulls with antlers, occur resting on the surface of the plant bed 

 No. 3, and at various levels in the brownish clay. Near the top of 

 the latter they are often found broken, and in one case antlers found 

 embedded in the top of the brown clay and protruding into the 

 grayish clay No. 5 were scored " like a striated bowlder." 



This grayish clay, or loam, as I should call it, consists exclusively 

 of mineral matter derived from the disintegration of granite. Dur- 

 ing its formation there can have been no soil on the neighboring 

 hills, and weathering must have been intense. It is practically un- 

 fossiliferous, but Mr. Williams records finding a reindeer's horn in 

 it. From all these characters it is difficult to escape from his con- 

 clusion that it represents a very severe climate. Since it is sepa- 

 rated from the horizon of the upper bowlder clay by more temper- 

 ate deposits, it must represent a return of cold conditions, after an 

 interglacial period. 



A similar section occurs at Craggah, near Ballah, County Mayo 

 (Williams, 1881), lacustrine beds with Irish elk being overlain by a 

 chocolate-brown detrital clay derived from the wearing down of the 

 coal measures, the whole being covered by bog. 



Underlying the peat bogs over a large part of the central plain of 

 Ireland are white or blue lacustrine marls, w^hich Mr. Williams 

 attributes to the same cold period, on the ground that abundance of 

 moisture would dissolve and subsequently precipitate great quanti- 

 ties of carbonate of lime, but this seems erroneous, for the marls are 

 really shell marls, and presumably a high temperature is more favor- 

 able to fresh-water shells than a low one. Remains of Irish elk are 

 frequently recorded from these marls (those described as from the 

 base of the peat bog are in most if not all cases really from the marl) 

 and this also seems to place them on the horizon of the lacustrine 

 clay of Ballybetagh. 



The memoirs of the Geological Survey contain many descriptions 

 of postglacial detrital deposits which seem to demand a far more 



