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ME. S. S. BUCKMAN OK CEETAIN JUEASSIC [Feb. I9IO, 



4. Certain Jtjeassic (' Ineeeioe Oolite ') Species of Ammonites and 

 Beachiopoda. By S. S. Btjckman, F.G.S. (Read November 3rd, 

 1909.) 



[Plates IX-XIL] 



Contents. Page 



I. Introduction 90 



II. Descriptions of Ammonites 91 



III. Descriptions of Brachiopoda 99 



IV. Summary 106 



I. Inteodttction. 



The species described or mentioned in the following pages have a 

 more or less definite connexion with the Jurassic strata of the 

 Dorset coast described in the foregoing paper l ; but, although this- 

 communication is offered as an Appendix to that one, it may 

 perhaps more rightly be regarded as an Appendix to that and the 

 other communications on similar strata mentioned on p. 53. 



The Inferior Oolite rocks are so remarkably prolific in species 

 of Mollusca and Molluscoids — there is so great a number of species 

 yet awaiting description — that there seems to be an idea among 

 those who have not studied the rocks in the field, that they receive 

 a kind of preferential treatment in this respect. Another explana- 

 tion may be suggested — that our judgment as to the time occupied 

 in the forming of the so-called ' Inferior Oolite ' strata is warped 

 owing to their tenuity — that they represent a time during which 

 destruction of strata was particularly active, therefore the remaining 

 deposits are only the fragmentary representatives of a whole. 



This is particularly the case in Dorset. A schoolboy once de- 

 fined a net as a series of holes strung together, and the Dorset 

 Inferior Oolite might be defined as a series of gaps united by thin 

 bauds of deposit. And one reason for the prolificness of the 

 deposits is that the amount of deposit can be no indication of the 

 amount of time, as show 7 n by the changes in successive faunas ; 

 and also that the deposits are so local — the deposits of one place 

 correspond to the gaps of another. Therefore many localities have 

 to be placed together to produce the full tale of the Inferior Oolite. 

 The very local distribution of Inferior Oolite species often means 

 that strata of particular dates have only been preserved in a few 

 favoured localities. 



The beds of the ' Inferior Oolite,' in a restricted sense, have now 

 been divided as deposits of about twenty-two successive dates or 

 hemeraa. 2 The total for the whole of the Jurassic would not be 

 more than about eighty-five, or perhaps, on an extended scale, a 



1 Alluded to as ' the stratigraphical paper.' 



2 See the stratigraphical paper, p. 55. 



