REPORT OF MEETINGS FOR 1902 227 



Monograptus pandus. 

 „ priodon. 



,, sedg?vickii. 



In addition to these, the following species are recorded in 

 the Geol. Survey Memoir on The Silurian Rocks of the 

 Southern Uplands, p. 209 : — 



Monograptus galaensis. 



,, convolutus. 



,, harrandei. 



,, leptotheca. 



Diplograptus sinuatus. 



These are far more than sufficient to fix the age of these 

 rocks with precision, as they include the three graptolites 

 which are characteristic of this geological horizon, which are 

 Monograptus crispus, M. exiguus, and M. turriculatus, none 

 of which is known to occur in any rocks except of the age 

 to which these are assigned, 



Close to the " Annelid Quarry " occur two or more remarkable 

 examples of dry valleys, the origin of which has been a fertile 

 source of discussion amongst geologists. One party thinks that 

 there is nothing wonderful about them, and that they are 

 no more than ordinary river courses, which, by some accident, 

 have been deserted by the streams that made them. Another 

 party thinks that they have been formed by the prolonged 

 action of the overflow from old glacial lakes existing 

 here at the close of the Age of Snow, when the ice of the 

 North Sea ponded back the waters which were escaping from 

 the melting of the ice inland. Another party, taking note 

 of the fact that the direction of these depressions coincides 

 exactly with the line of march known to have been followed 

 by the moving ice throughout a lengthy period of the Age 

 of Snow ; and taking note, further, that many similar grooves 

 even now bear glacial markings in their lowest parts — these 

 geologists conclude that they are mainly of glacial origin, 

 and due to the mechanical erosion and modification by the 

 ice sheet of old pre-glacial land features. In other words, 

 that the furrows are of glacial origin. 



