18 New York State Mi 



material build up their hard parts, the organic precipi- 

 tates taking the form of shells, the skeleton of corals, 

 bones and other hard structures. Organic tissues when 

 properly buried become. altered, leaving a product which 

 is composed of a mixture of carbon and hydrogen, such 

 as coal which is a product of alteration of plant tissues. 

 Among the plants there are certain bacteria which live in 

 warmer seas and through chemical action bring about the 

 separation of calcium carbonate or lime from the sea 

 water in small spherical or elongated grains which upon 

 accumulation form a deposit of oolite. Oolitic rocks 

 resemble in structure the roe of fish and give a very 

 pleasing effect in building stones. Oolitic deposits due to 

 bacteria are forming along the coast of Florida in great 

 abundance. A number of species of algae or seaweeds 

 in the geologic past and today are lime-secreting or cal- 

 careous forms, a large part of the mass of coral reefs 

 being formed by them. Since many of these lime-secre- 

 ting seaweeds also precipitate a carbonate of magnesium, 

 the rocks formed are dolomitic in nature and, as pointed 

 out above, become more so through solution of the cal- 

 cium carbonate content. The Lithothamnion of our mod- 

 ern coral reefs also formed extensive limestone masses 

 in the past. Coralline is a common lime-secreting sea- 

 weed along our coast. The fresh-water stonewort 

 (Chara) not only forms deposits of marl on the lake bot- 

 toms today, but is responsible for limestone beds in past 

 ages. A calcareous seaweed (Cryptozoon) forms reefs in 

 our Upper Cambrian rocks (Little Falls dolomite) which 

 are well exposed in Lester Park and other areas around 

 Saratoga Springs. Silica deposits of organic origin are 

 far less common than organic lime deposits. Diatoms, 

 plants of low organization, have silicious skeletons which 



