132 A YEAR OF COSTA RICAN NATURAL HISTORY 



from this place July 15, 1909, proved to be porphyritic basalt lava with 

 small plagioclase phenocrysts, while other fragments, one centimeter 

 and less in diameter, from the same place and date, are volcanic lapilli 

 of scoriaceous lavas, basalt and pyroxene andesite apparently. The 

 Arctostaphylos, lupine, myrtle, and Ericad are more partial to the coarser 

 parts of the floor. In craters G and H there are bare vertical rock faces, 

 but with these and the exceptions noted above under vr and Ir, the walls 

 and floors of the craters are of loose cinders of varying size. 



The only other published sketch-plan of the craters of Irazu of whose 

 existence we have been able to learn is that of Dr. Karl Sapper (1901). 

 As may be seen by comparing his much more detailed plan with ours, the 

 two differ considerably, yet are sufficiently alike to enable one to iden- 

 tify the various craters represented. No doubt Dr. Sapper's sketch is 

 more accurate than ours, in spite of his description of his own as "eine 

 approximative Veranschaulichung." We have left our sketch as it was 

 originally drawn except that we have changed our lettering of the different 

 craters to conform with his. Dr. Sapper considers granddaughter crater J 

 to be really a part of the floor of the western daughter-crater (III), grand- 

 daughter crater E to be younger than D, and G and H to be the youngest 

 of the granddaughters. 



Two sections through the craters of Irazu have been published by 

 Prof. Tristan in his 1910 paper on the volcano. 



We add a list of approximate altitudes from Dr. Sapper's paper, " Die 

 siidlichste Vulkane Mittelamerikas " (1901). 



Designation Diameter Altitude of Rim 



I (Urkrater) 1200 3414 and less 



II (Ostkrater) 500X400 3230-3380 



III (dritter 800X700 3230-3320 



Hauptkrater) 



A 3170 



B 3160 



C 3170 



D <3 160 I enclosed 



[ by a rim 



E 3150 j 3160 



F <3i90 



G 3 200 



H 3 200 



