548 Dr. J. R. Kinahan on the Genus Oldhamia. 



tinguish them from the pseudomorphic shapes masses of crystals often assume. 

 First : their symmetrical regularity of form, this having a constancy of direction 

 as regards the bedding, not passing through it in every direction, as crystals 

 always do. Second : the mode of their occurrence, abundantly, yet not univer- 

 sally, distributed through the beds, the fossils bearing a uniform relation to the 

 line of stratification of the beds in which they occur. Third : the permanency 

 of character of the fossils, even when the beds are situate in localities at 

 great distances from each other, and are dissimilar in their chemical and physical 

 constitutions. Fourth : the constant occurrence of the fossils in beds whose 

 formation is due to aqueous action ; in certain portions only of these ; and 

 almost always in company with traces of undoubted remains of animals of 

 aquatic habits, identical with archetypes existent at the present day. And, 

 lastly: the close agreement of the fossils in form with certain living aquatic types. 

 These characters conjoined supply a mass of evidence which render untenable 

 every theory which would assign to these fossils any origin save that before 

 stated, viz., that they are what are commonly called organic remains, and, ac- 

 cordingly, the genus Oldhamia is now recognised in all books on Palffion- 

 tology. 



Before proceeding to the consideration of the affinities of the fossil, it will 

 be but right to mention briefly the more important communications relative to 

 it published in geologic works, — a task fortunately comparatively light, as, if we 

 except its discoverer, the only author who has given us any information re- 

 garding it is Edwaed Forbes, — other authors contenting themselves, as far as I 

 can learn, with recording its existence, without any notice of its mode of occur- 

 rence or structure. 



The earliest reference to this fossil will be found in the " Journal of the Geo- 

 logical Society of Dublin" for 1844. In an abstract of a paper on the Rocks 

 at Bray Head, by T. Oldham, Curator of the Society, afterwards Professor of 

 Geology in Trinity College, and now Director of the Indian Geological Survey, 

 where, in combating the idea that the great rock mass now called Cambrian was 

 primary, the author states that he " had not as yet been successful in finding orga- 

 nic remains in the slate rocks Bray Head, with the exception of some small zoophy- 

 tic markings, which did not appear referable to known genera." — vol. iii. p. 68. 



The next notice occurs in the same Journal, an abstract of a paper read 

 15th November, 1848, " On Oldhamia, a new genus of Silurian Fossils," by 



J 



