494 R. TATE ON THE LIAS ABOUT RADSTOCK. 



The Lower Lias is reduced in this district to 24 feet, as contrasted 

 with the 300 feet or more assigned to it in other areas : 

 this is due either to attenuation of its subdivisions or to denu- 

 dation of a portion; and though both causes seem to have played a 

 part, yet it is to poverty of sediment that I ascribe the first con- 

 sideration. If this be so, then it must be conceded that the zones of 

 Ammonites are consequently compressed, and that species are brought 

 into so near superposition as to be almost in juxtaposition. But, so long 

 as they are superimposed, the order is uncontroverted, and it would 

 be escaping from conviction to declare them to be mingled together. 

 I dare assert that the succession of Ammonite-life is as much en regie 

 in the Radstock Lias as in the most typical districts, though the con- 

 trary has been maintained. This being the case, there is no need to 

 discuss the question as to whether or not the absence of a zone consti- 

 tutes a proof of unconformability, as it has been supposed to do 

 upon wrong premises in so far as relates to this district*. 



Attempts have been made to invalidate the importance of zoolo- 

 gical zones over a wide area, though it is generally admitted that 

 they are applicable to special localities. In the criticisms that have 

 been called forth adverse to the law of succession, minor considera- 

 tions have been allowed to outweigh the generalizations of a larger 

 experience, and the critics have based their arguments more fre- 

 quently than otherwise on faulty observations. Incorrect identifica- 

 tion of species and inferring the position of fossils from their matrices 

 are the chief sources of error. When Ammonites Charmassei is con- 

 founded with A. angulatus, then the range of the latter is greatly 

 elevated ; when A. Sauzeanus is called A. spinatus, then that species 

 is made to traverse the whole of the Middle Lias and a great part of 

 the Lower Lias ; when A. fimbriatus is recorded as A. cornucopice, 

 then an associate of A. communis is seen in company with A. Jame- 

 soni. Notices of similar mistakes might be multiplied ; but I have given 

 sufficient to show upon what unstable foundations are based some of 

 the arguments of the opponents to the docrine of zoological zones. 

 The practical value of a knowledge of the distribution of species in 

 the Lias has been recognized in the Cleveland district. 



Lower Lias. 



I will now give the Radstock section of the Lower Lias by way of 

 illustrating my opinion regarding its subordinate groups. 



* Moore, Quart. Journ. Geol. Soc. toI. xxii. pp. 459, &c. Woodward and 

 Blake, Geol. Mag. vol. ix. p. 198. 



