October 12, 1906.] 



SCIENCE. 



467 



of the source, and will be the same as if that 

 were viewed directly. In other words, the 

 change of wave-length depends on the rate 

 of change of optical path from the source to 

 the receiving apparatus. If the source is sta- 

 tionary and the mirror moved the effect is 

 doubled whether the mirror is plane or curved. 



The fallacy in Dr. Heyl's suggestion ap- 

 pears to lie in his considering a moving image 

 as in all respects equivalent to a moving 

 source. While this may be true as a proposi- 

 tion in geometrical optics, there is the essen- 

 tial physical .distinction that the phase of the 

 vibrations issuing from an image depends not 

 only on the vibrations of the original source, 

 but also upon the (optical) distance from that 

 source. Doubtless if we were to follow the 

 image with our spectroscope we should observe 

 a change of wave-length due to the latter 

 cause. However, even if we could surpass 

 the feat of hitching our wagon to a star by 

 hitching our instruments to the much more 

 swiftly flying image, we should again have 

 the same effect as if the source were viewed 

 directly. 



Horace Clark Richards. 



Randal Morgan Laboratory of Physics, 

 University of Pennsylvania. 



SPECIAL ARTICLES. 



GLACIAL STAGES IN SOUTHEASTERN NEW ENGLAND 

 AND VICINITY.^ 



For some years the writer has been engaged 

 on the problem of the differentiation of the 

 Pleistocene deposits of Long Island and south- 

 eastern New England. Some of the results 

 have already been published,^ and reports dis- 

 cussing in greater detail the subdivisions 

 recognized, and their correlation are in prep- 



^ Published by permission of the director of the 

 United States Geological Survey. 



- ' Probable Representatives of the Pre-Wiscon- 

 sin Till in Southeastern Massachusetts,' Jour. 

 Geol., Vol. 9, 1906, pp. 311-329. ' Probable Pre- 

 Kansan and lowan Deposits of Long Island, New 

 York,' Am. Geol., Vol. 32, 1903, pp. 308-312. 

 ' Geology of Fishers Island, New York,' Bull. 

 Geol. Soc. Am., Vol. 16, 1905, pp. 367-390. ' Clays 

 of Cape Cod,' Bull. 285, U. S. Geol. Survey, 1906, 

 pp. 432-441. 



aration. The completion of the reports, how- 

 ever, owing to the assignment of the writer 

 to other lines of investigation, is likely to be 

 considerably delayed, and it has, therefore, 

 seemed advisable to present a brief statement 

 of the Pleistocene succession in the region in 

 question, as it is understood by the writer, in 

 the columns of this journal. 



Pleistocene Subdivisions. 

 In the area examined, which includes Long 

 Island, Gardiner's Island and Fisher's Island, 

 New York ; Block Island and the coast of 

 Rhode Island, and Martha's Vineyard, Nan- 

 tucket, Cape Cod and the coast of Massachu- 

 setts northward to Boston, the Pleistocene 

 events appear to have been as follows: 



1. Deposition of the Deeply Oxidized Tills 

 and Weathered Gravels. — At Brockton and 

 Stoughton, in Massachusetts, and other points 

 in the vicinity, there are several exposures of 

 bright yellow or red till composed of the dis- 

 integrated remains of local rocks occurring 

 in protected spots beneath the younger tills. 

 In most cases these old tills rest on deeply 

 weathered rock surfaces, and are believed to 

 represent preglacial residual soils slightly re- 

 worked by the first ice advance, which appears 

 to be pre-Kansan in age. 



On Long Island the Cretaceous is overlain 

 unconformably by several hundred feet of 

 yellow-stained gravel containing a few deeply 

 weathered or disintegrated granitic pebbles 

 and an occasional erratic crystalline boulder. 

 It was originally correlated with a part of the 

 Pensauken of New Jersey, but was later given 

 the name Mannetto by Yeatch. It is believed 

 to be pre-Kansan and to represent the outwash 

 of the same glacier which further inland de- 

 posited the till described in the preceding 

 paragraph. 



2. Long Period of Subareal Erosion. 



3. Deposition of Granitic Gravels. — These 

 gravels were noted in 1903 by Yeatch in the 

 well borings of western Long Island, and in the 

 following year were recognized by the writer 

 in the cliffs of Block Island, Martha's Yine- 

 yard and Cape Cod. They have a maximum 

 thickness of 100 or more feet and consist of 



