THUNDER-EGGS AND GEODES — BROWN 331 



to distinguish between them is the reason for the marked but friendly 

 difference of opinion we held regarding their origin and meaning. 



The algal specimens cut from pillars or cylinders that for years 

 had been erroneously called geyser cones, as I have already explained 

 (Brown, 1949), originated by the deposition of lime incident to the 

 life processes of algae around woody snags lodged along the shores 

 of Eocene and Miocene lakes in Wyoming and Nevada. Hess sent a 

 batch of sections of this Nevada material to a noted algologist and 

 received in reply the correct information that algae indeed were in 

 large part the cause of the laminated effects there seen. Whether 

 or not he sent sections of the igneous spherulites to the same or other 

 students of algae I do not know. Be that as it may, he felt sufficiently 

 encouraged to believe that algae also were responsible for the filaments 

 seen in thunder-eggs. My purpose now is to define my position about 

 these colorful and fascinating plantlike objects; and I hope to do 

 this without blemishing Hess's memory or ruffling the feelings of those 

 of his rockhound friends who believe as he did about these things. 



FILAMENTS IN THUNDER-EGGS NOT ALGAE 



The advocates of the algal theory to explain the "growths" in 

 thunder-eggs deceive themselves in two ways. First, they mistake 

 striking but superficial lifelike resemblances for the real thing. Yet, 

 so closely do these filaments imitate natural growths that self-decep- 

 tion about them is understandable and pardonable, especially for 

 persons untrained in botanical identification. Observant examina- 

 tion of the delicate filaments with a good hand lens or a binocular 

 microscope shows that when well developed they are tubular. They 

 are not segmented or jointed, that is, with cell after cell in linear 

 rows, as they should be were they the filaments of fresh-water algae. 

 Exceptions among such algae are the partitionless greenhouse Vau- 

 cheria and the parasitic Phyllosiphon, but neither of these in other 

 fundamental respects is comparable to any filaments seen in thunder- 

 eggs. Significant also is the fact that no spores or other reproduc- 

 tive structures have been recognized as such among the supposed 

 algal filaments. 



Unlike those of algae the filaments in thunder-eggs are individually 

 very variable in diameter and in erratic branching (pi. 5, fig. 4; pi. 6, 

 fig. 3). They thicken and thin irregularly in an unalgalike manner 

 throughout their extent; and their most notable surface feature is 

 a more or less conspicuous, although sometimes much subdued, warti- 

 ness and tumescence (pi. 5, fig. 4; pi. 6, fig. 2) that gives them the 

 appearance of microscopic intestines (pi. 4, figs. 3, 4). These minute 

 swellings along their length indicate that the filaments and their 

 branches developed in successive pulses at their free ends. 



