338 Proceedings of the Royal Physical Society. 



The distribution of the shells in this deposit seems to 

 favour the same conclusion, for along the eastern seaboard 

 the shells are abundant, but they are more difficult to obtain 

 as the sections are followed inland towards Thurso and Eeay. 

 The appearances presented by these organic remains indicate 

 glacial abrasion precisely in the same manner as the stones 

 in the same deposit. This fact has been noticed by various 

 observers, and has been repeatedly referred to in connection 

 with the question of the origin of the till. They are broken, 

 smoothed, and striated like the stones associated wdth them ; 

 indeed they resemble the shell fragments we found in the 

 Orkney boulder clay, though in the latter case they are more 

 fragmentary and not so well preserved. The most common 

 forms met with are Cyprina Islandica, Mactra solida, M. 

 truncata, Turritella ungidina, Astarte ellij^tica, A. horealis. 

 But thouo'h the shells as a rule are more or less broken and 

 in many instances striated, yet in some cases entire valves 

 have been dislodged. Mr Jamieson found " one entire valve 

 of Astarte horealis, another of A. ellijotica, and two small ones 

 of A. compressa, likewise a specimen of Natica nitida, and 

 another of N. Islandica, both almost perfect." The striking 

 example of the complete bivalve Anemia, referred to by Mr 

 Jamieson and Dr James Geikie, was found by Mr C. W. 

 Peach protected in the hollow of a stone. Indeed it is 

 highly probable from the appearances presented by many of 

 the fragile shells that they were frozen in the ground 

 moraine, and in this way escaped complete destruction. 



A glance at the accompanying list conclusively shows that 

 the sections have yielded but a small number of forms 

 characteristic of the littoral zone. After years of vigilant 

 searching, Mr C. W. Peach obtained only a few species which 

 lived along the shore, among which may be mentioned two 

 specimens of Purpura lapillus, a few specimens of Patella 

 vulgaris, Mytilus rarely, and Tapes pullastra also rarely. We 

 shall point out presently that the scarcity of these shore forms, 

 and the great abundance of species whose habitat lay in deeper 

 water, have an important bearing on the question of the 

 origin of the shelly boulder clay. 



