50 



THE GEOLOGIST. 



formly employed flint knives in sacrificing animals, and for circum- 

 cision. . From this absence of all reference to flint or stone weapons 

 in the earliest writings of the Welsh, it seems to follow, either that 

 the writings cannot be depended upon to supply precise information, 

 or that the men who made the flint weapons were of another race, 

 possibly much earlier inhabitants of the island. 



Thirdly, whence was the material obtained ? There are no flints 

 in the formations and strata of the vicinity, — that is certain. But 

 then they may be picked up any day by a careful search on the 

 shore ; and so may granite boulders and worn fragments of igneous 

 rocks. 



The chert of these implements is peculiar. It is of a dull, opaque 

 green colour, full of minute grey spots. I do not at present know 

 of any like it in these parts ; but one lump, tide-borne to the coast, 

 would have supplied all required for the sixteen fragments of this 

 kind found. 



CGBKESPOKDENCE. 



Age of the 'Blackdown Greensand. 



Sir, — The question as to the true position in the Greensand series of the 

 "Whetstone" deposits of Blackdown, in Devonshire, is one which, so long 

 as it remains uncertain, must naturally force itself upon every geologist 

 who either studies or collects the fossils of the Greensand formation ; and, 

 therefore, although this question is neither new nor of universal importance, 

 I trust that I may be permitted to refer to it in the present instance. 



The question is simply this — Are these (Blackdown) deposits equivalent 

 to the Upper Greensand, to the Gaulfc, or to a portion of the Lower Green- 

 sand ? or do they represent the whole of these in an exceptional form ? 



In parts of Xent or Surrey, where the Lower Greensand strata rest 

 upon Weald clay, and are everywhere separated from those of the Upper 

 Greensand by an intervening bed of Gault, such a question would be 

 readily determined. But at Blackdown the case is different, the Greensand 

 being there found to rest upon red marl, and the Gault either absent or 

 imperfectly developed ; so that, in default of the usual direct evidence, the 

 geologist must be content with such indirect conclusions as can be drawn 

 either from the general appearance of the deposits or from a comparison 

 of the organic remains with those contained in other portions of the Creta- 

 ceous series. Whether or not this last method has been carried out by 

 those who consider the Blackdown deposits to be of Upper Greensand age, 

 I have not hitherto been able to ascertain. 



In the British Museum all the Blackdown fossils are marked as Upper 

 Greensand, in the Museum of Practical Geology, more cautiously, as 

 Greensand ; while in both they are ranged side by side with fossils from 

 Warminster, — a locality where the Upper Greensand is well defined by the 

 presence of the Gault. JN"ow, supposing Upper Greensand deposits to pre- 

 vail equally at Blackdown and Warminster, one might expect to find a 

 considerable resemblance between the fossils from these two localities ; 

 yet, on comparing the specimens, the fact proves itself to be quite the 

 reverse ; for, at a rough computation, I fiud that out of 156* Blackdown 



* These and the following numbers refer to Mollusca only. 



