34 Traoisacticms. 



History of a Crichton Boulder. By J. Gilchrist, M.D., 

 Medical Superintendent, Crichton Royal Institution. 



The brief notes of this paper refer to a large stone which 

 is now lying to the N.E. of the female airing court, Southern 

 Counties Asylum, and which is denominated in geological 

 language a Boulder. A Boulder is a fragment of rock, 

 smaller or larger, as the case may be, from the size of the 

 head to that of a house. It exhibits at least two, not unfre- 

 quently three characteristics : 



1. It is rounded. 



2. It is polished. 



3. It is often striated. 



These characteristics serve to distinguish a Boulder from 

 other varieties of rock. 



The first characteristic indicates that since the fragment 

 was detached from its parent mass it had been subjected to 

 the action of some influence which had modified its appear- 

 ance, rubbed off its angles and rounded its form. Its polished 

 condition indicates a greatly prolonged action either erf the 

 same or some other power. The third — the striae — indicate 

 the action of a peculiar agent very different from that which 

 produced the first or second characteristics. The agent en- 

 gaged in the production of these results is obviously enough 

 Water — as the waves of the sea, the currents of a river, &c. — 

 either in its ordinary fonn as water or in its extraordinary- 

 form as ice. 



The striae on a true boulder are always in straight lines, 

 indicating necessarily the action of a solid body in a given 

 direction. Such action, therefore, obviously can never be 

 attributed to w^ater or to water and ice, for the action of 

 these agents, single or combined, is to obliterate, not to pro- 

 duce such lines. In short, the only agents in nature known 

 to be capable of producing such results are 



A Glacier or an Iceberg. 



