June 30, 1905.] 



SCIENCE. 



989 



northeast and southwest or northwest and 

 southeast. A third series of breaks running 

 nearly due north is also at times in evidence. 

 The faults are most often the result of differ- 

 ential movements causing even a marked 

 sheeting of the rocks. The faults run out 

 into the Paleozoic areas, and are shown with 

 diagrammatic distinctness, where they have 

 been especially described by H. P. Gushing. 



The problem of the drainage is of especial 

 interest. All the waters go ultimately either 

 to the Hudson or the St. Lawrence. The 

 courses of the large streams follow sometimes 

 the older type of valleys, sometimes 'the later. 

 Barriers of drift have often driven them from 

 their old lines across low, preglacial divides 

 into new ones. The courses of the Hudson 

 and Onondaga are particularly striking illus- 

 trations, each exhibiting one or more marked 

 bends to the eastward. The courses of the 

 two were described and discussed in some 

 detail. 



The different types of lakes were also de- 

 scribed including the river valleys ponded 

 by barriers of drift, the fault valleys and 

 the relations to the older type of depression. 



The nature of the ice invasion and its modi- 

 fying effects were passed in review, chiefly 

 along the work of I. H. Ogilvie. With a brief 

 statement of the Post-glacial lake-fillings, etc., 

 which have been especially set forth by C. H. 

 Smyth, Jr., the paper closed. 



The Paleo geography of Mid-Ordovicic Time: 

 Charles P. Berkey. 



Both the Cambric and Ordovicic formations 

 contain prominent sandstone strata alter- 

 nating with dolomites wherever exposed in 

 Michigan, Wisconsin, Minnesota, Iowa, Hli- 

 nois, Missouri, Arkansas and Indian Terri- 

 tory. The northern margin, however, is pre- 

 vailingly more arenaceous than the southern, 

 where shales replace many sand beds. At still 

 greater distance, in Ohio, Kentucky and Ten- 

 nessee, these are in turn represented by lime- 

 stones largely. 



The uppermost one of the series is the St. 

 Peter. This sandstone, as well as each of the 

 more important ones below, is believed to rep- 

 resent an extensive retreat and re-advance of 



the sea. Few marks of the erosion intervals 

 are preserved. Only here and there has the 

 mantle of sand permitted much attack upon 

 the underlying dolomite, and the reworking of 

 the sands themselves has obliterated most in- 

 ternal evidence of such history. 



Much of the sand, furthermore, is wind- 

 blown. This reworking by the sea and the 

 wind is believed to be the chief cause of the 

 extreme purity of the St. Peter. 



The St. Peter stage of the Ordovicic, there- 

 fore, represents a retreat of the Mississippian 

 sea from the vicinity of Lake Superior to 

 probably as far as Ohio, southern Illinois and 

 Arkansas, followed by a readvance to its 

 original position. The northern part of the 

 St. Peter contains a sedimentary break. In 

 part it is both older and younger than the 

 same formation in its southern extension, 

 while, on account of the reworking accom- 

 panying the sea advance, there is greater con- 

 formity with overlying than with underlying 

 beds. A. W. Grabau, 



Secretary. 



At the meeting of May 1, 1905, Vice- 

 President Hovey presiding, the following 

 papers were read: 



The Pleistocene Beds of Sankaty Head, Nan- 

 tucket: J. Howard Wilson. 



When visited by early explorers, the section 

 at this locality was kept freshly exposed by 

 the cutting back of the bluff by the sea, but 

 for quite a period of years this has been pre- 

 vented by the northward extension of the 

 Siasconset apron beach, so that the face of 

 the bluff is now covered with talus and over- 

 grown with beach grass. 



The locality was visited during the summer 

 of 1904 and considerable work done in ex- 

 posing the section and making a collection of 

 the fossils. 



This work resulted in the collection of 81 

 species, 21 of which had never been reported 

 from this point, including Pandora crassidens 

 Conrad not previously found in any horizon 

 above the Miocene, and Serripes laperonsii 

 Deshayes and Macoma incongrua Von Mar- 



