Fossil Shells in the Drumlins of the Boston Basin. 487 



showed* that the similar but more impressive occurrences in 

 Great Britain, where shells are found in the till to a maximum 

 height of 1350 feet above the sea, do not require a submerg- 

 ence of the land or any change of level ; but rather that the 

 shells and fragments of shells found on the mountains of 

 Wales, etc. had simply been plowed up by the ice-sheet during 

 its passage across the bed of the Irish Sea and incorporated 

 with the normal drift. The shells are thus to be regarded as 

 preglacial inhabitants of the Irish Sea, and they owe their 

 present positions entirely to the agency of the ice-sheet. 



Three years later, Upham applied this theory to the explana- 

 tion of the shells in the till of the Boston Basin. \ He exam- 

 ined many of the till sections in and about Boston Harbor, and 

 proved that the distribution of the shells is very restricted, and 

 that in no direction are they found far beyond the present 

 limits of the harbor, adding seven new localities and four new 

 species to what were known before. His tabulated list shows 

 for the most prolific of the new localities, Peddock's Island, 

 five species, as against eighteen then known for Great Head, 

 Winthrop. Upham also pointed out more clearly than had 

 been done before for this region the usual conditions of the 

 occurrence of the shells, viz : in more or less fragmental forms 

 in the entirely undisturbed, unmodified and unoxidized till. 

 The shells are to be found, as a rule, only in deep sections, 

 simply because they have been gradually removed from the 

 superficial, oxidized till through the solvent action of meteoric 

 waters. 



In this Journal for February, 1894, Mr. B. E. Dodge has 

 added four species — Lunatia groenlandica, Scapharca trans- 

 versa, Buccinum undalum, and Ilyanassa obsoleta — to those 

 previously found at Great Head, bringing the list for that 

 locality up to twenty-two species, or twenty-five species for the 

 entire Boston Basing six species only being known from points 

 outside of Winthrop, three of which are included in the 

 Winthrop list. Mr. Dodge was, apparently, not aware that 

 one of the present writers§ had previously published a list of 

 eleven species found in the drumlins of the Nantasket penin- 

 sula, this list including three of those named by him as new 

 for Great Head, viz : Ilyanassa obsoleta, Buccinum undatum, 

 and jScapharca transversa, and one other new species, Cruci- 

 bulum striatum. 



* Report of the British Association for Adv. of Sci., Birmingham, 1886, pp. 

 632-635; Am Naturalist, vol. xx, pp. 919-925, November, 1886; this Journal, 

 III, vol. xxxii, pp. 433-438. December, 1886. Also, see American Geologist, vol. 

 ii, pp. 371-379, December, 1888. 



f Proc. Boston Soc. Nat Hist., vol. xxiv, pp. 127-141. 



% Mr. Dodge has made these numbers 23 and 26, respectively, but this appears 

 to be an error in addition. 



§ Occasional Papers, Boston Soc. Nat. Hist., vol. iv, p. 142. 



