1875.1 207 [Stodder. 



seven feet, seven and one-half feet, ten feet, eleven feet and four- 

 teen feet below the top of the bank ; besides one from the north side 

 forty feet below the top, from a bed apparently the continuation of 

 the fourteen feet bed on the opposite side, the hill being higher on the 

 north side. The first specimen, at five feet depth, -was surrounded 

 by the roots of a large tree standing on the summit of the bank, and 

 contains numerous vegetable fibres. 



All the specimens are similar in appearance (except that from 

 fourteen feet in depth, which is much darker) of a light drab color 

 very like clay, very low specific gravity, a little heavier than water, 

 and more or less stained, apparently by iron, which seems to act as 

 a cement. Now they are dry they are hard, but not so hard that 

 they cannot be crushed in the fingers. The forty feet specimen from 

 the northerly side has the darker color of the fourteen feet sample. 



I have cleaned and prepared for microscopic study portions of the 

 five feet, eleven feet, fourteen feet and forty feet samples. Some are 

 more difficult to clean than others, the iron cement adhering very 

 tenaciously, and being very difficult to remove. 



The upper layers present, as might be anticipated, more differences 

 from the others than they do from each other, viz., there is a smaller 

 proportion of organism, and larger of mineral, I estimate about 

 twenty per cent, organic and eighty per cent, sand, with many vege- 

 table fibres and roots. The diatoms are in a more perfect condition, 

 a larger proportion being whole and uninjured, while in the deeper 

 layers they are more broken, the fine fragments of the siliceous 

 valves exceeding in bulk the entire or whole frustules. The lower 

 layers contain from fifty per cent, to eighty per cent, of organic forms 

 of which the Diatomacese constitute by far the greatest part. 



The deeper we go, the larger is the proportion of debris or broken 

 frustules. There was so little variation in the contents of the speci- 

 mens examined that I have not undertaken the great labor of clean- 

 ing the other specimens. 



I annex in a tabular form a list of the species identified in the 

 different layers. From this it will be seen that there is no essential 

 change of forms from the lowest until we come to the upper or five 

 feet layer, indicating that during all the time required for the gather- 

 ing of this great accumulation of these minute remains there were 

 no great changes of physical conditions to influence the life and 

 growth of these forms. The five feet layer then gives indications 

 that some changes were taking place, by the disappearance of genera 

 or species that flourished in earlier periods. 



