158 JF. B. Wright— The Drumlins of South Donegal. 



in the western part which lies right in the lee of the hills. The 

 eastern part lias rounded drumlins, the western crescentic and 

 triangular drumlins. It is suggested that gradual change of direction 

 produces the rounded forms and sudden change the triangular and 

 crescentic forms. 



Further, there is a complete absence of cresting in this area of 

 oscillation. The drumlins are smoothly domed and often subdued in 

 prufile. Change in the direction of the ice-motion seems to prevent 

 the production or else the preservation of crests. 



The ideas discussed above as arising out of the evidence cited mav 

 be summarized in the following propositions, which, however, are not 

 regarded as proved, but are only put forward tentatively in order that 

 their applicability to, other areas may be tested. 



Fig. 5. Contour map of the drumlin topography west of Ballintra, co. Donegal. 

 The drumlins, numbered 1 to 5, are marked with corresponding numbers 

 in Fig. 4. Nos. 1, 3, and 4 are typically crested drumlins with serrated 

 profile. They are also forked at the downstream end. ' No. 2 is of half- 

 cigar form. Contours every 25 feet, taken from the Ordnance Survey Maps. 

 Scale 3 inches = 1 mile. The arrow shows the direction of ice-motion. 

 Reproduced by permission of the Controller of H.M. Stationery Office. 



1. Drumlins are built up by the addition of material mainly along 

 the median line. 



2. If this addition of material is continued until the complete 

 withdrawal of the ice or until the cessation of the ice-motion, then the 

 drumlin is left with a crest. 



3. If on the other hand the addition of material ceases before the 

 ice-motion, then the latter imparts to the drumlin a smoothly rounded 

 outline. 



4. In areas where the ice-motion is constant in direction the 

 resulting drumlins are elongated. 



5. If on the other hand the direction of ice-motion is continually 

 changing, the resulting drumlins are shortly oval. 



