ACADEMY OF NATURAL SCIENCES. 271 



Mr. Dall made some remarks on the shells which have been col- 

 lected by various naturalists at and near Monterey. 



He remarked that be himself had collected in two weeks no less than two 

 hundred and nineteen species, which number, added to forty-four which have 

 been previously reported as occurring there, but which he did not obtain, gives 

 two hundred and sixty-three as the whole number of species of shells now 

 known to have been found at Monterey. 



Of these were previously obtained only to the south of Monterey, twenty- 

 four ; previously obtained only to the north of Monterey, forty-two ; previously 

 obtained to north and south, but not at Monterey, twenty-nine ; previously 

 obtained at Monterey, one hundred and one ; not obtained by Mr. Dall, forty- 

 four ; new, or not reported, twenty-three. 



Collections of shells are greatly needed from points between San Francisco 

 and the mouth of the Columbia river, and also from points between San Diego 

 and Cape St. Lucas, in order to determine questions of geographical distribu- 

 tion. 



A curious fact was noticed in Chiton scabra, of Reeve, which, although be- 

 longing to a class of strictly marine animals, was observed clinging to the rocks 

 beyond the teach, except in storms, of the highest spray. That it does not 

 migrate is proved by the fact that, living in nooks and crevices of the rocks, 

 it grows into the very form of the hole in which it lives. 



Mr. Dall also mentioned that, having visited and thoroughly searched the 

 original locality for Helix Californiensis, a small island off Point Cypress, 

 accessible only at low tide, this species was found to be nearly exterminated. 

 A letter received from Dr. Canfield of Monterey since the visit of Mr. Dall, 

 confirms the fact of the extinction. This has been caused apparently by a large 

 millipede, which exists in great numbers, and is extremely voracious. 



Several of the shells found commonly at Monterey, are identical with others 

 collected during the past season on the coast of Russian North America. 



Professor Whitney made some remarks on the absence of the 

 Northern Drift formation from the western coast of North America 

 and from the interior of the continent, throughout the region to 

 the southwest of the Missouri River. 



The term " Northern Drift " is understood to include the masses of unstrati- 

 fied detrital materials and holders which have been transported and distributed 

 by some general cause independent, in a great degree, of the present conforma- 

 tion of the surface and of the direction of the existing river courses. The 

 investigations of geologists have shown that the surface of Canada, New Eng- 

 land, and the States north of the Ohio and north of the parallel of 39°, as far 

 west as the Mississippi, and even for some distance beyond it in that direction, 

 are covered by detrital materials which have been carried from the North 

 towards the South, and often for a great distance and in immense masses. 



The explorations of the Geological Survey of California have demonstrated 



