﻿54 CEKTAIN JURASSIC STRATA OF SOUTH DORSET. [Feb. I9IO. 



(10) 1901. ' Homoeotnorphy among Jurassic Braehiopoda ' Proc. Cotteswold 



Nat. F.-C. vol. xiii, pp. 231-90 & pis. xii-xiii. 



(11) 1903. 'The Toarcian of Bredon Hill, & a Comparison with Deposits 



elsewhere' Quart. Journ. Geol. Soc. vol. lix, pp. 445-58. 



(12) 1906-7. Monogr. Inf. Ool. Aram., Suppl. (Pal. Soc.) pp. cciv-ccix. 



(13) 1898. The Author (& others). ' Excursion to Bridport, &c.' Proc. Geol. 



Assoc, vol. xv, p. 293. 



(b) Chronology. 



In the various communications enumerated in the foregoing' 

 Bibliography, I have shown how it is possible to date the Jurassic 

 strata with very great precision, and I have given various tables of 

 chronology. The plan of more numerous chronological or zonal 

 divisions has been adopted by various geologists, both in this country 

 and on the Continent : even further refinements than I had made, 

 though not always than I had anticipated, have been proposed and 

 used. 



The Table of Chronology, which it is proposed to employ in the 

 present paper for dating purposes, is given below. A partly similar 

 table has appeared already l ; but, as modifications of nomenclature 

 have been introduced by other workers, and are now suggested by 

 myself, republication seems desirable. Further, opportunity is taken 

 to add what may be described as the prominent Ammonite facies of 

 each date, employing for the purpose terms as concisely descriptive 

 as possible. This addition may not only be a guide for field- 

 workers, but it may illustrate what a fine museum exhibit could 

 be made of the stratigraphical-zoological sequence of the different 

 Ammonite facies ; because not only is such a sequence proved in 

 the main for Europe, but there is good reason to suppose that it 

 obtains on the other side of the Atlantic and in Japan. 



Of the hemeral names tabulated here, three are new : one, 

 Shirbuirnia, is due to refinement in generic nomenclature, and two, 

 scJtloenhachi and Ancolioceras, arise from greater precision in chron- 

 ology ; they will be discussed later. 



How with opportunity for the examination of thick deposits of 

 strata the want of great refinement in stratigraphical or chrono- 

 logical nomenclature makes itself felt, is shown in a recent paper 

 by Dr. Mascke. Where I have made one division he has made 

 nearly four. 2 A copy of his interesting table is appended (Table II, 

 p. 06), where he compares his divisions with mine. The difference 

 is explained by the fact that in North Germany Mascke has 

 something over 140 feet to study, whereas in this country we 

 have in the most favoured localities less than 5 feet, and at most 

 localities a few inches or nothing. All the same, the possibility 



1 ' On the Grouping of some Divisions of so-called " Jurassic " Time ' 

 Quart. Journ. Geol. Soc. vol. liv (1898) table i, facing p. 450. 



2 Just as I am about to present this paper, Mr. Beeby Thompson very 

 kindly sends me some MS. showing that he is doing the same for the Upper 

 Lias. This matter is dealt with later (p. 85). 



