232 Reviews — Glaciation of East Lothian. 



tarn is pointed out where a change of slope occurred along one of the 

 grooves. Attention is also called to the presence of large transported 

 masses of Carboniferous Limestone, in one case one-third of a mile long 

 and a quarter broad. 



Turning to the phenomena attending the retreat with occasional 

 re-advances of the ice-sheet, the authors remark, " Thus step bj^ step 

 the enveloping ice shrank back to leave the Lammermuirs standing 

 like a stone in the midst of melting snows ; and stage by stage the 

 memorials of this retreat were furnished by the obstructed drainage of 

 the hill country, joined by the waters issuing from the glacier itself." 



The phenomena in question did not affect the higher portions of the 

 Lammermuir Hills ; they indicate the action of water impounded in 

 front of the retreating ice-sheet, and serve to explain the anomalous 

 drainage system, which could not have been produced under any 

 existing circumstances. The peculiai'ities of the surface features were 

 observed more than forty years ago by Professor John Young and 

 Sir Archibald Geikie, and the latter suggested that they might be due 

 to the modifying influence of direct glacial erosion. Thus instances 

 were given of narrow glens or ravines, quite dry, and open at each 

 extremity, along which, with the present configuration, no stream 

 could ever have flowed. The present authors point out that many of 

 the tj'pical examples of these deserted ravines have been excavated 

 entirely in drift deposits, and cannot therefore be vestiges of a pre- 

 glacial drainage system. They are, in fact, overflow channels which 

 have been cut by glacially diverted waters, and have failed in later 

 times to retain streams. 



There are, however, numerous glacial drainage - channels still 

 occupied as watercourses, and to these special attention is drawn. 

 They exhibit a marked tendency to the formation of ' corroms ' 

 and the consequent establishment of short cuts. The term corrom 

 (cothrom), as remarked by the authors, is a Gaelic word used in 

 place-names in the Ardgour district of Argj-Ushire to denote a delta- 

 watershed. Its literal meaning is a 'balance,' and it is intended to 

 illustrate that a stream issuing upon such a cone has the chance of 

 flowing either the one way or the other. In the present district it 

 has been found that there are many cases where a tributary stream 

 has thrown out a cone or delta into a deserted glacial drainage-channel 

 and established a watershed within it. 



The authors deal with these highly interesting features, and 

 describe the later erosion that has been produced by streams that have 

 been left in occupancy of glacial drainage-channels. This erosion is 

 seen in the winding gorges that have been carved on tbe floors of 

 some of the ancient valleys. 



It should be mentioned that the authors use the term corrom in 

 reference to function and not to origin; remarking that "many 

 a great beheaded valley must have found itself in just such plight, 

 and accepted a corrom as the watershed of its lower reaches." 



The memoir, which is issued to the public at 4«. 6^., is illustrated 

 by four beautiful photographic plates, a colour-printed map, and six 

 text-illustrations. 



