1889-90.] PELOTECHTHEN BALANOIDES. 215 



1. It grew on the mud in a quiet sea. I do not think sponges grow or 

 ever did grow except on rocks. 



2. The formation appears simpler than that of sponges. 



Imagine a thing not unHke in shape the puff-balls of our meadows, a 

 lump or a bladder surrounded by an envelope of cellular structure, the 

 whole enclosed in a tough skin, growing in numbers, in the dark mud — 

 without a foot stalk : the mud would at times be deposited in such quan- 

 tities as to kill the zoophytes — which would account, if nothing else did, 

 for their differences in size : they are from the bigness of a hen's egg to 

 that of a coal scuttle. 



The fact that the ring of cellular structure has become filled with py- 

 rites should cause no wonder, nor should the form of the crystals ; the 

 pyrites have replaced the older filling by infiltration — a not unusual 

 process in rocks of such great age. Examples exist of early sponges 

 having had their spiailm replaced by pyrites in much later rocks than 

 these. 



The PelotecJitJieii is found throughout the argillites for sixty miles 

 from Thunder Cape to the Silver Mountain, and doubtless further. I 

 have the authority of Mr. Chas. E. Eschweiler that it is not unfrequent 

 among the rocks of the Keeweenaw peninsula — the iron pyrites there being 

 replaced by copper. 



