﻿536 S.V. Wood,jiin. — Aynerican and British Surface- Geology. 



comparison it is noticeable that the soundings obtained from this 

 area also resemble the rock under examination in the comparative 

 rarity of Pulvimdina Micheliniana, one of the commonest of Atlantic 

 Foraminifera, and in the scarcity of the arenaceous types. But little 

 care was taken, in the process of washing, to preserve the Eadiolaria, 

 but such as remain are of the same species as those of the line of 

 dredgings alluded to. 



In conclusion, it appears to me not too much to say that after 

 disintegration and washing this "Chalk" from the New Britain 

 Group could not possibly be distinguished by its organic remains 

 from a washed Globigerina-ooze dredged in 1500 to 2500 fathoms 

 in the South Pacific. The determination of the exact geological age 

 is a matter for geologists ; my observations have necessarily been 

 limited to the physical characters and the organic constituents of 

 the specimen placed in my hands by Prof. Liversidge, but it appears 

 worth considering whether the rock may not be part of a recent sea- 

 bottom which has been distributed by volcanic or other agency. 



Such deposits may be very old chronologically speaking, and we 

 know by dredging experience that they do often become very hard 

 and compact even comparatively near the shore. Mr. Brown's letter, 

 quoted above, provides us with the required disintegrating force. 



III. — American " Surface Geology," and its Eelation to British. 

 With some Remarks on the Glacial Conditions in Britain, 

 especially in Reference to the " Great Ice Age " of Mr. 

 James Geikie. 



By Searles V. "Wood, Jun., F.G.S. 



(PART II.) 



{Continued from page 496.) 



NUMEROUS buried channels filled with drift occur over Ohio and 

 the neighbouring states forming the St. Lawrence basin. Some 

 of these penetrate the water-parting, and formed, according to Prof. 

 Newberry, waste weirs through which the lake watei's of the St. 

 Lawrence basin escaped into the valley of the Mississippi, as the 

 land rose and the sea retired from that valley. This, if I understand 

 him rightly, took place after the beds 3a had been formed, and 

 before the terraces, to be described under the number 4, began to 

 form by the fall of the lake waters ; but these waste weirs would 

 seem to have probably acted the same part also at an earlier period, 

 viz. during the commencement of the Erie clay deposit, when the 

 lake began to form by the recession of the ice from the water-parting, 

 and when it must have been full up to the brim of that parting, or 

 at least up to the level of the waste weirs. 



The final shrinking, however, of the waters of the lake-basin is 

 marked, according to Prof. Newberry, by the formation of clearly- 

 marked terraces or lake- beaches at successive levels, the uppermost 

 of which inosculates with these waste weirs. The shrinkage giving 

 rise to them may have arisen, he says, from the removal of ice-dams 



