IxXxii PKOCEEDINGS OE THE GEOLOGICAL SOCIETY. 



not altogether unimportant characters, or even two series of indi- 

 viduals which constantly differ from each other by one or more 

 decided characters, belong to two species, or at least must be 

 provisionally treated as such. This principle is, in fact, according 

 to my views, the only one which can preserve science from mis- 

 chievous errors and confusion. But I do not pretend to say that 

 it is founded on the natural idea of species. My own conviction, 

 based on many years' careful study of Tertiary shells, is rather 

 this, that species, at least within the range of natural groups, do 

 not always remain distinct, but rather arise by sometimes slow, 

 sometimes quick (I do not mean sudden) modifications, caused 

 by new conditions of life, by gradual change, and perhaps even 

 by crossing of former species." 



In conclusion he calls attention to the very remarkable features 

 of this assemblage of fossil life, consisting of 200 species from 

 ninety-five different genera. It consists of specimens from every 

 zone, littoral and deep-sea, those living on rocks and sea-weed, 

 in bays and estuaries, on mud and sand. It is a mixture of 

 European Miocene species, with recent species of Southern Africa 

 and the East Indies ; and considering the short, time during which 

 they were collected, he is convinced that they do not represent 

 one half of the real Tertiary fauna of these Atlantic islands. 



In addition to his labours on the British Brachiopoda, on which 

 he has been so long engaged, Mr; Davidson has described, in the 

 'Annals and Magaziae of Natural History ' (July 1864), seven 

 species of fossil Terebratulse from the Maltese Islands. This 

 account is given as an appendix to an outline of the geology of 

 these islands by Dr. L. Adams ; and, according to the most recent 

 researches, they are considered as portions of an early Miocene, 

 equivalent to the Hempstead beds in England. It is, however, a 

 remarkable fact, that|of these seven species, four, namely, Terehra- 

 tula minor, Phil., Terebratiilina caput-serpentis, Linn., Megerlia 

 truncata, Linn., and Argiope decollata, Chemn., are now found living 

 in the Mediterranean. In the description of Terebratula sinuosa, 

 Brocchi, a well-known large species, some very valuable remarks 

 are introduced respecting the confusion caused by the various 

 synonyms under which it has been described. 



Since the time when Mr. Lonsdale gave us so much valuable 

 information respecting fossil corals, no one has worked harder or 

 more successfully in this field of palseontological research than 

 our Secretary, Dr. Duncan. I shall not attempt to give you an 

 analysis of the several interesting papers which he has communi- 

 cated to us during the past year ; but there is one part of the 

 subject on which he has brought forward so much new and im- 

 portant matter, that I must briefly allude to it here*. I refer to 

 that paper in which he describes the process of mineralization 

 which the corals have undergone, and which ends in some cases 

 in such complete silicification that all traces of structure are de- 

 , stroyed, and they are finally reduced to pure homogeneous black 

 * Quart. Joiirn. Gleol. Soc. vol. xx. p. 358. 



