DESCRIPTION OF THE DEPOSITS 315 



as shown in plate 15, figure 2. The trench in the foreground is in fos- 

 siliferons chiy, while the drills are working in slate ledge. The two meet 

 at an altitude of about 160 feet. 



There are, however, areas of clay at levels of 200 feet or over. It has 

 been suggested that these are of either fluviatile or marine origin. It is 

 my opinion that in this area, at least, they are of glacial origin and should 

 be mapped as till above the l()0-foot level. Owing to tbe large amount 

 of clay in this till, its general similarity to the clays ])elow, its high alti- 

 tude, and continued cultivation, there is no topograplric feature to mark 

 the boundary between these tw^o formations. However, it is my experi- 

 ence that in most cases there will be more boulders present above the 

 160-foot level, or else there will be large stone heaps showing a large 

 amount of clearing over wliat may seem to ])e a rather level clay plain. 

 In one case I saw several granite boulders, 2 feet or more in diameter and 

 deeply striated, which had recently been removed from one of these higher 

 clay plains. I can, however, offer no conclusive evidence as to the origin 

 of these clays. 



PITYSWAL CHARACTER OF THE CLAY 



According to Sawyer, who examined the foundation for the AYaterville 

 High School when the building threatened to sink i]i the "(piicksand" — 

 that is, the marine clay — ^^the principal component is an impalpable gray 

 powder with the characteristics of feldspar. Therefore the sample is not 

 a true clay, but owes its claylike properties to being composed of very 

 finely divided rock flour, mechanically ground from feldspathic rocks, 

 such as granite or the metamorphic slates and schists." The boring from 

 which these samples were taken passed through about TO feet of this clay, 

 ending in fine to coarse sand. 



Fossils are fairly common in good exposures of the clay and in places 

 are abundant. They may occur merely as casts or with the shell sub- 

 stance preserved. In this latter, case the epidermis may still persist 

 (Portlandia glacialis, MytiJus edulis, . Astarte elliptica, and Astarie 

 striata), and even the elastic ligament {Astarte elliptica). These fossils 

 will be described more fully later in the paper. 



The marine clays either grade or change abruptly into sands. AMiere 

 the clay overlaps the esker gravels, the cla}- may disappear entirely toward 

 the summit of the esker, leaving the sand resting directly on gravel. 

 Such is the case in the locality illustrated in plate 13, figure 2. Within 

 100 feet of the point shown here, and about 5 feet higher, the sands rest 

 on gravel. These sands are very free from loam and blow readily into 

 dunes when the vegetative cover is removed (see plate 16, figure 1). The 



