872 REPORT— 1898. 



be reached as to the value of the three different kinds of fossils — Plants, Invertr;- 

 brates, and Vertebrates — in determininpr the age of strata. All evidence of this 

 kind is of value, but it is the comparative value of each group that is the impor- 

 tant point I -wish to emphasise ; and I have brought the matter before this Section 

 of the Association in the hope that a better understanding on this question may 

 be reached among geologists in the interest of the science to vt^hich we are all 

 devoted. 



2. On Aggregate Deposits and their Relations to Zones. 

 By Rev. J. F. Blake, ALA., F.G.S. 



An objection is sometimes made to the classification of strata in zones — by 

 means of certain fossils — that cases are known in which the characterising fossils 

 of more than one zone occur together in the same band of rock. It is sometimes 

 replied to this, that a careful search will show that these fossils occur in their 

 proper position even in this single band, the older type being found near the bottom 

 and the younger near the top. Without denying the partial truth of this, the 

 author regards these multizonal bands as having a special character which removes 

 them from the ordinary type of deposit, for the subdivision of which the method 

 of zones has been adopted. Zones are best observed in massive uniform deposits 

 such as the Lias, Oxford Clay or Chalk, the formation of which has been continuous 

 through the life-history periods, or hemerre, of several species, which lie in the 

 deposits in their natural position, as they would fall to the bottom, or lie there, at 

 death, and be successively covered by subsequent portions of the deposit. These 

 multizonal bands, however, do not differ from this type simply in the smaller 

 amount of contemporaneous deposit, but show signs of being formed in a different 

 way altogether. The fossils do not lie in a natural position, but often stand on 

 end; they are not arranged in horizontal bands, but are confusedly mixed 

 together; and they include broken fragments often of a rmianie character, and 

 these are in many cases of a considerable size. These peculiarities are considered 

 by the author as evidence that the deposit was a tumultuous one, in which the 

 material was drifted rapidly by strong currents in a horizontal direction. They 

 are in fact the sweepings of the bottom of the sea from the places where the fossils 

 originally lay, where they may or may not have been covered by deposit. It is for 

 this reason that the fossils in them belong to various dates, the actual deposit 

 itself being necessarily at least as young as the latest fossil it contains. The 

 author therefore proposes to distinguish such deposits as aggregates. 



Whereas ordinary deposits, especially those in which zones are best marked, 

 indicate tranquil deposition with the conditions remaining long unchanged, these 

 aggregates indicate a marked change of conditions, and therefore in ail probability 

 the commencement of a new group of rocks. For this reason they are of consider- 

 able importance. The author's attention was specially directed to these aggregates 

 in Russia, where they are found at the base of a series, by some considered to be a 

 continuation of the underlying Jurassics, and by others to be the commencement of 

 the Cretaceous rocks. There are, however, many instances of them in this 

 country, as at Ilminster, where they are called Upper Lias ; also the ' cephalopod- 

 bed' of Gloucestershire, and the 'junction bed' above the Middle Lias on the 

 Dorsetshire coast. Similar phenomena ai'e reported from the base of the Cretaceous 

 beds at Beer Head ; and it is probable that the Faringdon sponge beds and the 

 Neocomian nodule beds of Potton are of the same character. They are also 

 reported from various localities in France and elsewhere on the Continent. 



3. The Geological Structure of the Malvern and Ahherley Ranges. 

 By Theodore Groom, 3f.A., D.Sc. 



In the district between Abberley and Bromesberrow two types of geological 

 structure are distinguishable. 



On the east is a comparatively undisturbed geological series ranging from the 



