64 THE CONNECTICUT AGRICULTURAL 



The Composition of Trap Rock. 



" New Britain, Ct., June 13, 1882. 

 " I enclose a sample of the stones and pulverized matter with 

 which our soil abounds. I desire to know if it contains potash or 

 phosphate of lime. I presume you can tell at a glance, but if an 

 analj^sis is necessary I hope you will make it. This trap rook 

 abounds in all this region. I had an impression that such rotten 

 stone as I send you is rich in all the mineral elements of plant 

 food. John B. ♦Smith." 



It has not been possible hitherto to make an analysis of the 

 sample of decayed trap rock sent by Mr. Smith, and the following 

 answer to his inquiries was based on the general result of such 

 investigations on the subject as have come to the writer's knowl- 

 edge. By Trap Rock is meant the " blue stone " which forms 

 the material of East and West Rocks at New Haven, of the 

 Hanging Hills of Meriden, and of many similar elevations along 

 the valleys of the Connecticut and Quinnipiac Rivers, 



Answer. 



The rest of the rock consists of silica, alumina, and oxide of iron. 

 The trap rocks are commonly verj slow to disintegrate, some 

 that contain much iron decay more rapidly. During the slow 

 decay, the lime, magnesia and alkalies become soluble in water 

 and wash away, so that the decayed rock is less rich in these sub- 

 stances than the original. The rock is a source of these forms of 

 plant food during its decay, more than afterwards. Still the fine 

 clayey matters that result retain small quantities of plant food, 

 such as you will find stated in the various soil-analyses that 

 have been published in the Station Reports. Phosphoric acid 

 remains mostly in the residue of the decay, and potash is washed 

 out much less relatively than soda and lime. The abundance and 

 vigor of the vegetation on such decayed rock, provided sunlight 



