Collections of the Academy. 25 



The most beautiful of our minerals are the agates 

 banded in their various colors. When polished, as the 

 large number of our collection is, they are very beauti- 

 ful. So many colors blended together in bands of differ- 

 ing shades and thickness, and they are only the common 

 quartz with iron, manganese or other minerals mixed, 

 which produce such different colors and shadings. There 

 are many other species of minerals in our cases which 

 I have not spoken of. 



Thus far I have spoken almost entirely of the inor- 

 ganic forms of mineral, that is, those that have never 

 been a part of living animal or vegetable beings. With- 

 out vegetable life we should miss nearly all our great 

 beds of iron ore, as iron held in solution in water is only 

 rendered insoluble and thrown down as sediment near 

 decaying vegetation. Our specimens of petrified wood 

 were once parts of trees growing where we find them in 

 Arizona today. Our great quarries of even-bedded lime- 

 stone are entirely the remains of animal life, such as 

 worn out shells, corals and bones of fishes or animals. 

 It is true there are many comparatively small deposits 

 of limestone in all parts of the earth made by the lime 

 deposits of hot springs and the dripping of water in 

 caves, and these are not organic. But the great mass of 

 limestone is entirely made of the remains of animal life. 



Of fossils, the remains of the animal life of the past, 

 while our collection contains a large number, we still 

 need many additions, especially those of the older forma- 

 tions. We have a few from the Palaeozoic age, but need 

 many more. From the Hamilton period of the Upper 

 Geodes of quartz, rough on the outside but lined with 

 large addition from these earlier forms of life would be 

 especially welcome. As we come up towards the later 

 geological formations, the Cretaceous, Tertiary and re- 

 cent periods, we have some very fine and unique speci- 

 mens. Our northwest part of Iowa, where not covered 

 by the glacial clnj or loess, is nearly all Cretaceous, from 

 which we have many fine fossils. From the clay of this 

 period, which is used in the numerous brick yards in this 

 region, many fine specimens have been found. In the 

 fall of 1887, workmen were digging a cistern on a farm 



