DIATOMS. 



DIATOMS are very small, one celled organisms, which are 

 among the primal forms of life, and have apparently ex- 

 isted with little or no change from the earliest appearance of 

 life upon the earth. 



They are bivalves with shells of glass instead of lime, held 

 together by side hoops of the same material instead of hinges. 

 For many years after their discovery they were supposed to 

 be animals, chiefly because of their power of locomotion, a 

 ver>' large proportion of them being rapid travelers during 

 their whole lives. Several eminent scientists still hold to this 

 opinion, but they are now generally regarded as belonging to 

 the vegetable world. They vary greatly in size and outline, 

 and are elaborately ornamented with sculptured markings, alae, 

 striae, costae, etc., many of them being among the most beauti- 

 ful forms in nature. Their shells being so largely silex they are 

 comparatively indestructible, and where the conditions are 

 favorable they often accumulate in vast quantities. Nearly 

 every permanent body of water, how^ever. small, contains them 

 in greater or less abuundance; wdien this water disappears the 

 diatoms are left as a fossil deposit. 



Quite a number of these deposits are found in Bristol. A 

 little over the line west of the lower reservoir of the Bristol 

 Water Company is one of these deposits ;the stratum of dia- 

 toms is about two feet thick and covers one or tw^o acres. It 

 contains numerous species many of them large and interesting. 

 When this reservoir was made, another fossil deposit w^as re- 

 moved. On the farm of Silas Carrington is another deposit 

 notable for the abundance of FrustiiUa Saxonica, well-known 

 as a test object for the microscope; its markings are so minute 

 as to require high powers and perfect lenses to resolve them. 



On the old Lazarus Hird farm is a deposit showing an 

 abundance of the very rare Achnanthidiiim vexellimi; and 

 north of this on the Mix farm is perhaps the largest deposit 



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