188 Correspondence — Mr, J. Lucas. 



bability of a nucleus now being formed among tbem, and discussed 

 tbe possibility of the earth's formation in a similar way. As con- 

 densation proceeded, and the earth became first fluid and then gra- 

 dually solid, he showed that we should have at the centre the dense 

 metals and their compounds, and in the crust the lighter metals, and 

 explained how it was that the sea was salt from the first beginning. 

 With a view to elucidate this part of the subject, he entered at some 

 length into the composition of the sun, whose condition now is strictly 

 comparable with that of the earth in its earlier stages, and proceeded 

 to show how exactly the metals and gases forming the sun's atmo- 

 sphere are ranged according to their densities. Coming more to 

 chemical geology proper, he showed how the first sedimentary rocks 

 were formed from the debris of pre-existing rocks, and the later ones 

 in turn from their debris. Alluding to the Bath hot-springs, he 

 strongly advocated the theory of their heat being due to chemical 

 rather than to volcanic action, and explained his reasons for believ- 

 ing that this action was owing to the oxidation of iron. Treating 

 amongst other heads of metamorphic action and mineral veins, — of 

 the first he demonstrated the probability of many of our metamorphic 

 rocks being due to the heat produ.ced by great mechanical distur- 

 bances, such as the crumpling up of strata, and not to contact with 

 the interior heat of the earth ; and of mineral veins he adduced 

 arguments in proof of their not being due to volcanic action. In 

 conclusion, he gave the results of a new experiment by Mr, Stoddart 

 of Bristol, which demonstrated very clearly the formation of flints, 

 and concerning which nothing was satisfactorily known. — H. H. W. 



coie-i^iESi^oisriDiBn^ciE, 



THE BOULDER-CLAY AND THE THAMES VALLEY. 

 Sir, — At the meeting of the Geological Society, on February 24thj 

 some surprise was expressed at the fact of the Boulder-clay not 

 crossing the Thames Yalley, It comes down in places to the water 

 level on the north bank (there the Thames Valley is older than the 

 Drift), and occurs nowhere along a distance of (I believe) ten miles 

 on the south bank. If, as seems highly probable, at the time when 

 the Boulder-clay was being deposited north of the Thames, parts of 

 Kent and Sussex were above water, the Thamas Valley could not 

 have been many fathoms deep, and existed as a channel running east 

 and west between an island to the south and a shoal to the north. 

 Along this channel an east and west current would flow parallel to 

 the northern shore of the island, and sufficiently strong to cut off" all 

 drift slowly travelling down from the north and prevent its ever 

 arriving at the coast. Therefore we find no remains of it now. 



J. Ltjoas. 

 Geological Survey of England, Upper Tooting, S.W. 

 February 26, 1869. 



DISCOVERY OF DAKOSAURUS IN ENGLAND. 

 SiK, — In the last number of the Quarterly Journal of the Geo- 

 logical Society appeared an abstract of a paper by Mr. Wood- Mason, 



