IV. DRILL-HOLE INTERPRETATION 



1. Generalized Stratigraphy 



Sampling techniques have been discussed in Section II. Samples were 

 given a preliminary inspection in the field upon removal from the split- 

 spoon sampler. This allows the driller to make decisions about sampling 

 interval and perhaps estimate the proximity of a significant sedimentary 

 change. 



The Drill-Log Appendix summarizes the preliminary field observations 

 and later binocular microscope analyses of the samples. Using the binoc- 

 ular microscope, estimates were made of grain size, sorting ^roundness, 

 and gross mineralogy. 



Examination showed a distribution of sediment that closely agrees 

 with previous work of Mclntire and Morgan (1963) and McCormick (1968) . 

 This study went beyond the depths of the McCormick study and added to 

 the interpretation of the geological history of Plum Island. The pale- 

 ogeography suggested by this study fits well with the ideas about submerged 

 relict dunes expressed by Anan (1971) . 



McCormick determined seven stratigraphic zones by analysis of marsh 

 cores. His generalized column follows: 



High salt-marsh peat 

 SpoPtina altemiflora peat 

 Western fine-grained facies 

 Eastern coarse-grained facies 

 Black peat 

 Weathered zone 

 Blue clay 



Mccormick's samples were studied by x-ray and grain-size analyses. 

 Such analyses were not made in this study, because it is more concerned 

 with the large-scale, more obvious, correlations. For example, results 

 of this study allow broader correlation (extension deeper and further 

 seaward) of such horizons as the weathered zone, which overlies the 

 glaciomarine clay sequence in McCormick's column. 



2. Glacial Till and Glaciomarine Clay 



Overlying the igneous bedrock surface is glacial till , which varies 

 from highly compact dnomlin material to extremely sandy till beneath 

 some of the beach deposits. Figure 28 is a photo of this sandy till 

 from hole CBB. Identification of this material as till is sometimes dis- 

 putable; the possibility that it is outwash or an ice-contact deposit is 

 acknowledged. However, the material is poorly sorted, angular, and the 

 pebbles have a silt cap-evidence that indicates till. The 



41 



