834 Handbook oj Nature-Study 



weakest, hornblende next, and feldspar is next to quartz, the strongest con- 

 stituent of granite. Water permeates the mica, hornblende, feldspar and 

 sometimes the quartz, and by its expansion in freezing causes the stone to 

 crumble. The reason why polished granite endures better than the rough 

 finished, is that the smooth surface gives less opportunity for the water to 

 lodge and freeze. When the weathered granite is cut up into small 

 particles by the waters of streams, they are sifted and all the parts which 

 are soluble are carried off, leaving a sand composed of quartz and mica, 

 which are insoluble. This sand is washed by streams into lakes, and then 

 is dropped to the bottom; if enough is thus carried and dropped, it forms 

 sandstone rock. All of our sandstones used for building purposes were 

 thus laid down. 



Cleopatra's Needle, which stood for thousands of years in the dry 

 climate of Egypt, soon commenced to weather and crumble when placed in 

 Central Park, N. Y. This shaft has a most interesting history. It was 

 quarried near Assuan, in the most famous of all granite quarries of 

 ancient Egypt. It was cut as a solid shaft in the quarry and carried 

 down the Nile River for 500 miles — an engineering feat which would be 

 hard to accomplish to-day, with all our modern appliances. It was one of 

 the obelisks that graced the ancient city of On, later called Heliopolis, 

 situated on a plateau near the present city of Cairo ; On was the city where 

 Moses was bom and reared. There .is still standing where it was first 

 placed as a part of a magnificent temple, the temple a part of a magni- 

 ficent city, one of these obelisks. It now stands alone in the middle of 

 a great fertile plain, which is vividly green with growing crops; a road 

 shaded by tamarisk and lebbakh trees leads to it; nearby is a sakiah, 

 creaking as the blindfolded bullock walks around and around, turning the 

 wheel that lifts the chain of buckets from the well to irrigate the crops ; 

 and a hooded crow, whose ancestors were contemporaries of its erection, 

 caws hoarsely as it alights on the beautiful apex of this ancient shaft, 

 which has stood there nearly four thousand years and has seen a great 

 city go down to dust to fertilize a grassy plain. 



LESSON CCXVII 

 Granite 



Leading thought — Granite is composed of feldspar, quartz and mica, and 

 often contains hornblende. 



Method — Specimens of coarse granite and a pocket knife are needed. 



Observations — i. What minerals do you find in granite ? How can you 

 tell what these minerals are? Look at the granite with a lens. How can 

 you tell the quartz from feldspar? Take a knife and scratch the two. 

 Can you tell them apart in that way ? How can you tell the mica ? How 

 can you tell the hornblende? 



2. What buildings have you seen made of granite? What monuments 

 have you seen made from it ? 



3. Which mineral in granite is especially affected by water? Which 

 remains unharmed the longest ? 



4. What is weathering? Mention some of the characteristics of 

 weathering. Why does the rough-finished granite weather sooner than 

 that which is polished? 



