18 



CAPE COD GEOLOGY 



In 1889 x in a geologic section illustrating Shaler's paper on the "Tertiary 

 and Cretaceous deposits of Massachusetts," I divided the Miocene at Gay Head 

 into two parts, described in descending order as follows : 

 5. Greensand beds and boulders of No. 4 

 4. Osseous or quartz pebble conglomerate 



The osseous conglomerate was represented as resting on eroded Cretaceous 

 beds, the age of which had been determined by means of White's work on the 

 fossil flora found at Gay Head. The beds of granitic gravel, sand, and boulders 

 that overlie the greensand were referred to an interglacial and preglacial stage. 



In 1897, in a paper on the unconformities of this part of the coastal plain, 2 

 I stated that the Miocene at Gay Head is made up of two well-defined lithological 

 divisions, and probably a third, which might be Pliocene. Dall later gave reasons 

 for so regarding it. The Miocene divisions were identified as the osseous con- 

 glomerate of Hitchcock, which was regarded as a basal member, and the supposed 

 later greensand, or foraminiferal bed. Rolled fragments of the osseous conglom- 

 erate were described as occurring in the basal part of the greensand bed, which 

 is found east of those parts of the cliff in which unbroken osseous conglomerate 

 is seen in place. The determination of the sequence of the deposits was based on 

 the occurrence of small boulders of the osseous conglomerate in the position in- 

 dicated. Up to this time no doubt had been expressed that the osseous con- 

 glomerate bed is a member of the Miocene series, as Lyell thought in 1842 and 

 Dall in 1895. 



In 1900 I published a notice of the finding of the astragalus of a fossil horse 

 in the osseous conglomerate at Gay Head in May, 1889. 3 H. F. Osborn, to whom 

 the bone was submitted for examination in 1900, expressed the opinion that the 

 bone was that of a Pleistocene type of horse, and the question arose whether it 

 was found in the osseous conglomerate or in an overlying bed of glacial gravel. 

 The statement was made that ' 'The bone was broken in extracting it from the 

 bed, and there can be no doubt about its occurrence as a constituent of the osseous 

 conglomerate." 4 On the same visit during which this bone was found, another 

 imperfectly preserved mammalian bone was collected from the osseous conglom- 

 erate in the same place, just east of the ' 'Devil's Den," in the folded beds figured 

 by Edward Hitchcock in his report of 1841, but this bone was not identified until 

 1916, when Dr. Glover M. Allen found it among the collections of the Museum 



1 Bull. Geol. Soc. America, 3, pp. 443-452, pi. 9, 1889. 



2 See bibliography. 



3 Woodworth, J. B., Glacial origin of older Pleistocene in Gay Head cliffs, with note on fossil horse 

 of that section, Bull. Geol. Soc. America, 11, pp. 459-460, pi. 42, fig. 2, 1900. 



4 Op. tit, p. 459. 



