330 Correspondence — Magister F. Schmidt. 



diggers. This positive testimony of coincident and uniform flint aggregation over so 

 large an area appears to be an important fact in its bearing on the origin of flint. 

 Mr. Bedwell had found the Ammonites entirely by trusting to the zone of life theory 

 insisted on by Mr. Caleb Evans in his paper on the Chalk (Geol. Assoc, 1870), and 

 had failed to find them until he had selected the faint line of flints as a datum line, 

 and worked from that. He advised all young students of the Chalk to examine a 

 cliff in true horizons, and not in a mere indiscriminate effort to make a lai-ge bag of 

 specimens ; to record carefully the exact chronological order of each fossil extracted, 

 by referring it to a datum line as suggested by Mr. Caleb Evans; to keep in mind the 

 time which may have separated the life history of two fossils, though only distant a 

 few feet from each other ; and to try and correlate two sections of Chalk rather by 

 the succession of zones of life in each cliff than by a mere comparison of indis- 

 criminately collected fossils. The author, in conclusion, urged the importance of 

 allowing Nature to teach her own independent lessons at the cliff side, of supple- 

 menting Nature by books rather than books by Nature, and pointed out how easy it 

 was for those having but little knowledge of details to be of service to Science, by 

 simply observing and following to its end one single thread, and one only, and then 

 laying the results before scientific men, leaving them 'to estimate the value of the 

 information. 



COiai2/ESI=>03iq"X)E3^0E]. 



NORTHEEN DRIFT ERRATICS. 



SiK, — I have lately been struck witli the idea that geologists living 

 in the midland and southern counties might like to compare the 

 erratics of their own neighbourhoods with stones from the Boulder- 

 clay of Cheshire, where the Northern Drift may be said to attain its 

 central and maximum development. I have therefore resolved to 

 devote next month (July) to the task of collecting small stones, 

 striated and cross-striated stones, chips from large stones, etc., naming 

 and assigning the parentage of specimens, and packing and sending 

 off boxfuUs to parties who may wish for them. There will be a 

 small charge to cover direct and indirect expenses. Those who are 

 interested in this subject would oblige by corresponding without 

 delay. 



Chester, June 13, 1873. D. MACKINTOSH. 



FURTHER REMARKS ON FTERASPIS. 



Sir, — ^I have lately succeeded in demonstrating the existence of 

 real osseous lucunse in Pteraspis, by preparing very thin horizontal 

 sections from near the upper surface of the shield. The lacunge are 

 very minute, and form, by their ramifications, a dense net- work, very 

 nearly resembling that in Tolypelepis undulatus, Pander (Monographie 

 der fossilen Fische der Silurischen Systems, tab. 6, f. 24), from the 

 uppermost Silurian strata of Oesel. I now regard that fossil as a 

 portion of a Pteraspidian shield, and shall search for further infor- 

 mation in that locality. 



As regards the supposed connexion between Pteraspis and 

 Cyathaspis on one side, and ScapJiaspis on the other, the evidence 

 furnished by Dr. Kunth's figures and description appear to me to be 

 most satisfactory. 



