164 Cincinnati Society of Natural History. 



8. Geology is encumbered with hypotheses, and observa- 

 tion in many cases is insufficient to settle definitely the 

 doubts. It then is left to synthesis to enlarge the field of 

 observation and to furnish definite solutions. Thus, the 

 origin of granite was one of the great problems confronting 

 geologists. The opinion that it was purely igneous prevailed 

 in the science for the first part of our cycle, replacing the 

 neptunist theor}^ of Werner ; but the difficulties were in- 

 creased a little later when, by means of the microscope, it 

 was found that the quartz was consolidated after the other 

 minerals, which was against the idea of a purely igneous 

 fusion of the granite. Elie de Beaumont ( 1S49) accepted the 

 intervention of water, and insisted, for proof, on the number 

 and frequency of the minerals sublimed on the periphery of 

 the massive granites. He supposed the water to be contained 

 in the form of inclusions in the quartz, a supposition which 

 was proved ten years later by Sorby, and gave thus a decisive 

 argument for the mixed origin of granite. When synthesis 

 was called in to answer the question, it proved conclusively 

 the impossibility of obtaining granite by purely igneous 

 fusion. 



II. METHODS OF SYNTHESIS. 



These methods will, of necessity, vary with the aim in 

 the mind of the investigator, but he must at all times bear in 

 mind the conditions outlined in the previous paper. The aim 

 is to imitate and form the minerals as in nature, under like 

 processes, using only such agents as can be positively affirmed 

 to exist in nature. While in very man}- cases high tempera- 

 ture, high pressure, and long time are required to form the 

 mineral, yet there is a large series of minerals formed under 

 ordinary conditions of pressure and temperature. In this 

 last group are found the sulphates, carbonates, phosphates, 

 zeolites, ores, and certain water-containing silicates. 



The influence of time is well illustrated in the case of cer- 

 tainly apparently amorphous precipitates, which, in a few 

 months, show small crystals, and in the course of a few years 

 form crystals of considerable size. 



For the purpose of description, the synthetical methods 

 will be divided into two general groups : i. The crystalliza- 



