222 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jail. 4, 



Dr. Norwood (Owen's Survey, p. 192) considers the great plutonic 

 chain north of Lake Superior, and running nearly parallel with its 

 north shore, from N.E. to S.W., to be the main axis of dislocation 

 for wide regions in this part of North America. 



This opinion is strengthened by finding in Rainy Lake, and along 

 the chain of lakes (225 miles long) which lead to the Grand Portage 

 of Lake Superior, that the dip of all the stratified rocks is almost in- 

 variably to the north* ; while that of the kindred rocks in Wisconsin 

 and Michigan, south of Lake Superior, is w^th great constancy to the 

 south ; and this over areas of many thousand square miles. 



Li hand-specimens the rocks of Rainy Lake are often not to bo 

 distinguished from those of Lakes Superior and Huron. Although 

 carefall}^ sought for, I met with no ores in Rainy Lake ; while in 

 Iron and Gunflint Lakes, on the east, indications of metalliferous rocks 

 are numerous. 



3. Oil some Swallow Holes on the Chalk Hills near Canter- 

 bury. By J. Prestwich, Jun., Esq., F.R.S., F.G.S. 



The occurrence of swallow holes on chalk and limestone hills is a 

 phgenomenon almost too well known and too general to call for any 

 special notice ; but there exists, in a locality not hitherto cited, near 

 Canterbury, a group of these stream-absorbent cavities of so remark- 

 able a character, that, as this question also bears so materially upon 

 the subject of the next communication I have to make, I beg to lay 

 before the Society a short account of them. 



I came upon this spot whilst tracing, a few years since, the 

 Thanet Sands through East Kent. Around Feversham and Can- 

 terbury the country consists essentially of chalk, but the high ground 

 between these towns consists of tertiary strata, forming a table- 

 land of a few square miles in extent. The area to be noticed is 

 merely that portion of the hill which lies south of the high-road, 

 and which is in part marked by a wood named on the Ordnance INIap 

 " Fish Pond Wood," extending over the London clay and Lower 

 Tertiary sands down to the edge of the chalk. The drainage from 

 this clay surface is carried off by several small brooks f having an 

 easternly or a southerly direction. It is to the latter that I would 

 particularly direct attention. Skirting the wood from Nick -hill 

 Farm westward to Lower Elmsden, there are to be found within a 

 distance of about a mile as many as six or seven of these water- 

 courses, all of which, without exception, disappear just within the 

 edge of the wood, in swallow holes, some of which are not more than 

 6 or 8 feet broad and deep, whilst others attain a diameter of 30 to 

 40 feet and a depth of 20 to 30. There is generally not much water 

 in the brooks running into these funnel-shaped % excavations, at the 

 bottom of which they form a small pool, that, notwithstanding this 



* The result of 120 observations in Rainy Lake, and of thirty in the other lakes, 

 carefully made by myself. 



t These brooks are not laid down on the Ordnance Map. 

 X On one side of which the stream forms a gap or lip. 



