11^2 Proceedings of (lie British Association. 



Dr. Ward exhibited specimens and drawings illustrative of impressions 

 of the feet of animals on the Greensill sandstone, near Shrewsbury. 

 Greensill Hill consists of a steep escarpment of new red sandstone, and 

 contains four strata that have been described by Mr. Murchison, and in 

 the second of which the impressions were found. This stratum, when 

 exposed to the atmosphere, always splits so as to exhibit ripple marks, 

 and on these marks the impressions of feet have been observed, as well 

 as marks of drops of rain. These last are often in an oblique direction 

 as if having fallen in a gale of wind, the direction of which is thus point- 

 ed out. The foot mai'ks differ from those of the Cheirotherium, in hav- 

 ing only three toes, armed with long nails, directed forwards, and not 

 spread out. Nothing resembling the ball of the foot has been observed 

 except in a few, which have some resemblance to the impression of the 

 foot of a dog. 



Dr. Buckland exhibited impressions in sandstone from Dumfriesshire. 



Mr. Knipe read a communication on a Trap Dyke in Cumberland. It 

 commences on the east side of the river Petterell, about six miles south 

 of Carlisle, and about two from the limestone quarry at Broadfield ; its 

 composition is like onion basalt, decomposing in concentric layers. It 

 passes by Great Barrock Hill and Armathwaite, crossing the River 

 Eden ; then by Combe's Peak and Stony Croft, Cringle Dyke, and Ren- 

 wick, about two miles from which last place a good vertical section of it 

 may be seen, on the west side of the Raven Water, which it crosses. It 

 is met with at Hastside Fell, cutting through the Pennine chain, its 

 eastern termination being about the source of the South Tyne River, 

 near which it appears to have altered the adjoining strata. Its length 

 is twenty-two miles, and its width from twenty to thirty yards. Its 

 course coincides with that of the great Cleveland Dyke, and it is not im- 

 probable that they may be connected; if so, a basaltic dyke, 120 miles 

 long, crosses our island from the Solway Firth to the German Ocean. 



A paper, ' On the Structure of Fossil Teeth,' by Mr. Nasmyth, was 

 then read, illustrated by several drawings. It had been stated by some 

 anatomists, that the proper dental substance consists of an uniform 

 structureless substance, and of fibres passing through it ; but the author 

 was led to believe that this structureless substance is organized, and 

 differently and characteristically in different animals, so as to be a 

 means of classification. He employed a magnifying power of the tenth 

 of an inch focal distance, with an achromatic condenser, and first found, 

 in the tooth of a fossil rhinoceros, the appearance of cells or compart- 

 ments, and afterwards found it to exist in recent teeth. He also examin- 

 ed the fibres of different teeth, and found that generally they presented 

 an interrupted or baccated appearance,as if made up of different compart- 

 ments, each class of animals presenting a different arrangement. 



In a paper read before the Medical Section, Mr. Nasmyth treated 

 more fully of the organization of the dental inter-fibrous substance, and 

 entered also into some details on the structure of the pulp. 



