400 DE. W, HIND AND ME. J. A. HOWE ON THE [Aug. IQOf, 



When the limestones are found in the shales above or below 

 the main development of the deposit, they are like the rocks 

 just described, or are softer and possess a more banded structure. 

 This banding is due to alternating layers of darker and lighter 

 material, the individual layers frequently being extremely attenuated 

 and very regular. In these softer rocks, thin streaks and layers of 

 darkly-stained cryptocrystalline silica are common, so also are 

 minnte cubes of pyrites ; no large organisms have been noticed 

 in the slides, and the microscopic ones are in a very bad state 

 of preservation. Indicatious of crinoid-stems and foraminifera 

 are seen in some of the slides ; always small, and generally indis- 

 tinguishable, their size may be indicative of adverse physical con- 

 ditions. The most prevalent organisms are sponges, represented 

 by small fragments of spicules, so abundant in some of the black 

 bands from the shales at the foot of the hill that they constitute the 

 greater part of the rock. They are either formed of calcite or, more 

 often, of the yellow silica. 



The essential feature in the hard rocks is the presence of casts in 

 clear calcite of small round bodies which are distributed 

 throughout the rock, sometimes sparsely, but frequently in great 

 profusion, and always standing out clearly against the dark back- 

 ground of the matrix. In no case have we yet been able to 

 distinguish any internal structure that could be relied upon with 

 certainty in allotting these bodies to their proper zoological position, 

 nor is there any trace of a limiting-wall remaining. At times they 

 appear as true, clearly defined circles, while at others the outline 

 is less distinct, the clear crystalline calcite passing irregularly into 

 the surrounding dark material. Spines of various sizes are common, 

 projecting from the circles, though they are not present universally. 



It is not without much hesitation that we suggest that these casts 

 may represent radiolaria, for in default of the characteristic 

 structure of the test it is not possible to give an absolute opinion. 

 They are usually associated with a few sponge-spicules. In thin 

 sections there is a very remarkable superficial resemblance between 

 these rocks with their calcite-casts and the radiolarian Culm rocks 

 described by Dr. G. J. Hinde & Mr. Howard Fox,^ or those from the 

 Devonian mentioned by Dr. Eiist.^ Dr. Hinde has very kindly looked 

 over some of our slides and admits the resemblance, though he could 

 not find any remains of the structure of the test. 



These calcite-casts, it will be observed, are always found in the 

 calcareous rocks, and their condition is in entire agreement with 

 the observations of Messrs. Hill & Jukes-Browne on the fossilization 

 of radiolaria in the Chalk and the Barbados deposits. Thus on 

 p. 604, Quart. Journ. Geol. Soc. vol. li (1895), they say : — 



' .... it will be seen that, while iu calcareous rocks where radiolarians are 

 indubitably present, it frequently happens that nothing but their outline 



1 Quart. Journ. Geol. Soc. vol. li (1895) pp. 609-67. 



"^ ' Beitr. zur Kenntniss d. foss. Radiolarien ' Palgeontographica, vol. xxxviii 

 (1892) pp. 113-14 et seqq. 



