438 ANNUAL UEl'OKT OF THE Off. Doc. 



REPORT CF THE MINERALOGIST. 



BY Col. Henry C. Demming. Mineralogist. 



CLAYS. 



The numerous clay deposits of Pennsylvania are being investi- 

 gated with more interest than at any time in the history of the 

 State. This is partly owing to publications by New York, New 

 Jersey, Maryland and Ohio, on the clay beds of those states, with 

 localities, names of owners, and analyses of products, together 

 with the uses to which the clays may be applied. It seems that 

 inquirers are not altogether satisfied with the clay productions of 

 those states, and are looking for something better in our own Com- 

 monwealth. Kaolins, ochres and paint clays are called for, with 

 an increasing demand for ''glue" clays, and light-colored plastic 

 varieties. A well prepared bulletin on Pennsylvania clays would 

 be widely sought for by residents of other states, and by those at 

 home interested in our argillaceous resources. 



SILICA SAND. 



The publication by this Board of the report on silicates one year 

 ago has had a marked effect for good, and more care is shown in 

 the selection of silica sand for mortar in plastering. Then more 

 deposits of good, pure sand have been found, and first grades can 

 be had at lower prices. This leads to purer plastering in newly 

 erected buildings, and to much less danger of defective flues in 

 chimneys. So pure and good have our best sands proved to be for 

 filtration purposes, that there is fair reason to believe they will be 

 adopted for use in the great sand filtration beds to be erected for 

 improving the water supply of New York City. 



CEMENT ROCK. 



The commercial introduction of Portland cement in the United 

 States has been followed by markedly increasing demand. 'So rapid 

 hate been the advances, and so substantial, that numbers of scien- 

 tific men are beginning to call this the cement age. Not only foun- 

 dations above and below water are made of cement, but whole super- 

 structures, including bridges, and some of our strongest and most 

 substantial railroad bridges. The sidewalks made of it are called 

 artificial stone, and so the street^ crossings and gutters. Various 

 tests are to the effect that the longer good cement structures are in 

 use, the stronger they become, until a maximum of strength is 

 reached excelling many kinds of natural building stone, and some- 

 times better than iron or steel. Many millions of dollars are in- 

 vested in cement manufacturing in our state, and many millions 

 more could be profitably used, if the known area of eem^'Ut rock were 

 enlarged. Now the work is confined, or nearly go, to the countiea 



