196 NEW YORK STATE MUSEUM 



size ranging from a dime to a half dollar. To pick up one of 

 these, well dried on the surface of the island and break it in half, 

 seems enough to convince the reflective mind at once of their 

 nature and mode of formation. It often contains as a central 

 nucleus a beach pebble of shale or limestone, a twig, or a bit of 

 charcoal from some youngsters' camp fire. About this a white 

 or greenish, travertine has been deposited in concentric layers 

 which show themselves with distinctness. Often the interior of 

 the cake is soft and powdery. Frequently the cake shows an im- 

 perfect fibrous structure. There is little doubt that this cal- 

 careous matter is constantly supplied by the influx of the lime- 

 charged waters of Sucker brook. The little island and its bar lie 

 directly in the course of this stream and receive the charge of 

 carbonate of lime before these waters have diffused themselves 

 over the wider surface and through the greater depths of the 

 lake to the south. It is only on the north side of Squaw island 

 that this water biscuit is found in abundance, and there almost 

 every pebble is a biscuit. This apparently simple mode of con- 

 centric deposition in the formation of these bodies is of itself 

 sufficiently interesting for record, and it would not be easy for 

 the writer to cite a parallel. Here is actually a coarse, un- 

 cemented oolite forming under peculiar but very simple condi- 

 tions. 



This however is not the whole story. On picking one of the 

 water biscuits from the lake bottom its surface is found to be 

 smooth, slimy and often greenish: exposure on the shore bieaches 

 it white. The calc-carbonate being dissolved in dilute acid and 

 entirely removed, there remains a soft, spongy, organic residuum 

 of precisely the volume of the original biscuit. From within 

 will drop out the nucleus, rupturing the side of the soft mass. 

 On examination, this organic matter proves to be a felted mass of 

 filaments of fresh-water algae, which have been examined for me 

 by Prof. C. H. Peck, the state botanist, and one of the species 

 identified as probably Isatis fluviatilis. In the judg- 

 ment of Prof. Peck there are several such species, and entangled 

 among them are to be found diatoms, the whole so reproducing 



