Occurrence of Boulder Clay at Huddersjield. 231 



we need not wonder at the difficulty of finding such an easily 

 denuded deposit as laminated clay on the precipitous slopes 

 of the Calder and Colne, especially when we consider how few 

 relatively, are the areas which have been exposed and ex- 

 amined. Foreign materials, Granite, Whinstone, etc., have 

 been reported from the Colne and Holme valleys, and though 

 these did not receive expert examination, it is probable that 

 part of the north-western Drift found its way into these valleys, 

 and further investigation may reveal its presence. 



Notwithstanding the fragmentary character of the evidence, 

 it is sufficient to enable us to suggest a probable explanation 

 of the deposits as we now find them. 



1. They probably belong to an early period of the Ice Age. 



2. The valleys were perhaps occupied by ice for a relatively 

 short period. 



3. The direction of the ice, and the rocks it passed over, 

 would account for the deposits being almost entirely composed 

 of rocks of the Millstone Grits and Lower Coal Measures. 



4. The valleys were pre-glacial in origin, and already con- 

 tained an alluvium with numerous water-worn pebbles and 

 boulders of Grit, Sandstone, Ironstone and Ganister. 



5. The long period during which the deposits have been 

 exposed to denudation, on the sides of valleys with precipitous 

 slopes, may well account for its present fragmentary character, 

 especially where the matrix was a sandy clay. 



6. If in later glacial times a lake was formed, the wash of 

 its shores would tend towards further denudation and re- 

 distribution of the material. 



7. The lake period was probably a short one, and laminated 

 clays, perhaps at no time in abundance, may have since been 

 obliterated, or remain undiscovered. 



8. Before the ice receded from the Pennine ridge, the rush 

 of melt-waters down these valleys might well have been 

 responsible for some of the features which render them of 

 peculiar interest. 



9. Evidences of super-deepening are not so pronounced 

 as in the valley of the Calder, which indicate that the present 

 land surface is two hundred feet lower than in glacial times. 

 In no part of the Colne drainage have the gravels been found 

 at so great a depth as in the Calder, but some of the tributaries 

 of the Colne, which drop steeply into the main valley, may 

 be in part thus accounted for. The gorge-like character of the 

 Colne, expecially where the river breaks through the Rough 

 Rock at Longroyd Bridge before entering the lower Coal Meas- 

 ures, is very suggestive. Similarly, but on a smaller scale, 

 the Meltham Brook has cut through the Rough Rock at the 

 ' Mag ' before joining the Holme. 



10. It seems probable that the broad band of alluvium 



1917 July 1. 



