286 Correspondence — Sir R. Oiccn — Mr. J. Gardner. 



rocks, the author stated, was impossible if peti'ological evidence was 

 of any value. The author also produced many facts to show that 

 the conglomerates at the base of the Cambrian constantly over- 

 lapped the different members of the series which he claimed to be 

 of Pre-Cambrian age, and that the unconformity was very marked 

 and to be clearly seen in many coast-sections. The conglomerates 

 were shown also to contain well-rolled pebbles of all the series in- 

 cluded under the names Dimetian, Arvonian, and Pebidian, as proved 

 by careful micros^copical examination of the fragments by Mr. T. 

 Davies and himself. An Appendix, by Mr, Davies, describing the 

 microscopic character of the rocks, accompanied the paper. 



C0I^I^:Es:F02^^ID:BIs^G:E. 



TJRIGLTFEUS, FEAAS ; AND TRITYLOBON, OWEN. 



Sir, — I have been favoured by Prof. Neumayr with an extract 

 from the " Neues Jahrbuch fiir Mineralogie," 1884, containing a 

 passage from the work by Prof. Fraas " Vor der Siindfluth." which I 

 regret not to have seen, and of which I add a translation. With the 

 above passage Prof. Neumayr adds a woodcut of the fossil tooth iu 

 question : — 



" Fraas describes in his work, ' Before the Deluge,' ' a peculiar 

 little tooth from the Bone-bed, near Stuttgart, under the name 

 Triglyphus, and he supplies the above figured very accurate wood- 

 cut of this unique specimen, which was, unfortunately, afterwards lost. 



" This Triglyphus corresponds in a marked manner with the 

 Tritylodon from the Cape ; both show exactly the same fundamental 

 type, although there are differences in the structural details and 

 there may be good reason for a generic separation. In both the tooth 

 is subquadrate the upper (masticating) surface is divided by two 

 deep furrows fi-om the front backwards into three longitudinal crests 

 resembling each other, each of which is again divided by oblique 

 incisions (cross furrows) into separate protuberances. It appears also 

 that the number of those protuberances nearly corresponds, as the 

 number in each row, " which come first in sight," is three, as well 

 in the one as in the other specimen. 



" Unfortunately we know only one tooth of Triglyphus, but it is 

 sufficient by its marked configuration to confirm a very remarkable 

 and close affinity between a South African and a central European 

 ' Trias mammal.' " Eichakd Owen. 



AEE THE BLACKDOWN BEDS THE EQUIVALENTS OF THE GREY 

 CHALK AT DOVER ? 



Sir, — A paper on British Cretaceous Nuculid^ was published in 

 the Quarterly Journal of the Geological Society for February. In it 

 I show (p. 14:2) that three out of four of the Grey Chalk species are 

 identical with those of Blackdown and with no others. Mr. Downes 

 has since this publication found what 1 believe to be the fourth species, 

 named N. pectinata, var. cretcB, at Blackdown, so that all the Grey 

 Chalk species are now known to be common to the two formations. 

 1 Vor der Sundfluth, p. 215. 



