BRITISH ASSOCIATION MEETING. 



461 



tmguished from that beneath, while, by the same means, the middle clay is with 

 equal ease separated from those clays above and below it. The rock dips 

 down to the south, and at a distance of three miles the middle clay is replaced 

 by sand. 



Eive miles north of Elsworth the St. Ires rock comes to the surface, and 

 dips to the east. It is a hundred and thirty feet beneath the Elsworth rock, 

 and very similar to it in mineral character. Its thickness is three feet, often 

 divided into two beds by a parting clay. It is brought up by an anticlinal, so 

 that on high ground four miles north the Elsworth rock is again met with. 



Six miles west of Elsworth is found the St. Neotts rock, which is deep down 

 beneath the St. Ives rock, though not so low as the zone of the Kelloway 

 rock. 



But for the breaks by these rocks, the lowest beds of Oxford clay would 

 graduate up, without any perceptible change in life, into the highest beds of the 

 Kimmeridge clay, the coral-rag being absent as such, but represented by a clay. 

 This clay contains a mixture of the fossils of the clays above and below, and 

 is met with above the Elsworth rock at Elsworth and Bluntisham. Erom the 

 exhibition at the latter place it is named the " Blunt'sham clay." The clay 

 beneath the Elsworth rock is the Oxford clay, so that the Elsworth rock is- 

 intermediate in position between that subdivision of the great clay formation 

 and the coral-rag. The fossils unmistakeably show it to belong to the clay 

 rather than the limestone formation, and hence it will be regarded as the 

 highest zone of the Oxford clay, while the St. Ives, St. Neotts, and Kelloway 

 rocks will serve to mark the several zones into which the formation is naturally 

 divided by its fossils. 



Thin rocks have also been met with in the Bluntisham clay in positions 

 which render it probable that they indicate divisions corresponding to coral-rag 

 and calcareous grit. 



ON THE PLEISTOCINE DEPOSITS OF NORTH AMERICA. 

 By Dr. Hector. 



The author stated, that his recent researches in that country afforded strong 

 grounds for supporting the view, that the diffusion of the erratic drift must have 

 resulted from the submergence of the north-east part of the Continent beneath 

 an arctic sea to a depth of nearly 3000 feet, and that the surface of the country 

 has received much of its present form by denudation during its re-emergence, 

 at first along sea-coast lines, and latterly along the shore lines of inland lakes, 

 which still exist, but of much smaller size than formerly. By the steppes which 

 have thus been found these deposits may be divided as follows : — 



Bordering the lower part of the valley of the St. Lawrence and extending 

 southwards through the valley of Lake Champlain, a marine deposit of boulder 

 clay has been described with mollusca, more arctic in their character than those 

 existing in the neighbouring seas at the present day. This deposit has not 

 been observed at a greater altitude than 600 feet,* and in its nature it would 

 seem to resemble those deposits that must be forming at present in Hudson Bay 

 and in the Arctic inlets and sounds, where the shore ice, kept in motion by the 

 winds and tides, acts like a pug-mill in reducing the previously deposited drift 

 to the condition of tough clay. 



On the shores of Puget Sound and the Gulf of Georgia, in latitude 49° N., 

 on the west side of the Continent, there are drift clays with boulders and 

 scratched rock surfaces, which, like those clays in the St. Lawrence Basin, do 



* Lyell, Rogers, Desor, &c, 



