242 Proceedings of the British Association. 



used in the attempt to determine the limits of genera and species by 

 the aid of the microscope. An experienced microscopic investigator, 

 Mr. Nasmyth, considered the minute structure of the fossil ivory in 

 Mr. Koch's collection of Mastodon bones, to indicate six or seven 

 species, while Prof. Owen, taking external characters, came to the 

 conclusion that all these remains were referable to the Mastodon 

 giganteus of Cuvier. 



* On the Agency of Land Snails in forming holes and trackways in 

 Compact Limestone,' by Dr. Buckland. — This notice was a con- 

 tinuation of one made at the Plymouth meeting, in which the author 

 ascribed certain perforations discovered by him on the under side of 

 ledges of limestone rock at Tenby, Boulogne, and Plymouth, to the 

 agency of an acid secretion of land snails, which resorted to these 

 perforations daily for shelter. The additional instances now describ- 

 ed were discovered by Dr. Buckland in Cumberland, during a visit 

 made in 1842, in company with Mr. Hopkins ; at Cannington Park, 

 in Somersetshire, by Mr. Baker ; in the string-courses of the Roman 

 castle at Richborough, built of Kentish rag; in the roof of the 

 cromlech at St. Nicholas, near Cardiff; in the rock work in Mr. 

 Dillwyn's garden, brought from Gower ; and in St. Mary's Abbey, 

 at York. Dr. Buckland exhibited specimens of limestone rock from 

 several localities, showing perforations occupied by snails, and grooves 

 or furrows leading to the perforations, and he insisted that these were 

 unlike those produced by any marine animal, or by atmospheric 

 causes. The perforated rocks were stated to be only found in dis- 

 tricts affording a rich vegetation, and were always met with imme- 

 diately on passing from a slate region, or one entirely composed of lime- 

 stone, into another covered with more luxuriant herbage. Dr. Buck- 

 land attached great importance to the perforations at Richborough 

 Castle, which, he said, afforded a measure of the time necessary for 

 such operations. The deepest holes he had seen in limestone rocks 

 never exceeded two or three inches, and he considered it probable 

 that they had occupied several thousand years in their formation ; 

 the holes were only found in the hardest limestone rocks, because in 

 all others they would be obliterated by atmospheric action. 



' On a Topographical and Geological Map of Mount Etna and 

 adjacent Country from actual Survey, 5 by Baron W. S. de Walter- 



