GEOL. VOL. I.] SMITH SANTA CAT A LIN A ISLAND. 45 



the entire rock. They are largely microscopic in size, with 

 here and there a larger fragment reaching an extreme length 

 of about .1 mm. This fragmental material is largely of 

 feldspar some of which shows twinning, besides an occa- 

 sional dull greenish patch of chloritic material. A few 

 quartz fragments occur, but the source of these may be the 

 quartzite of the basement series, as several fragments were 

 seen in one of the slides, composed of very small inter- 

 locking grains of quartz. Most of these fragmental crystals 

 show a feeble polarization, particularly the smaller ones. 

 In one of the slides were seen several larger fragments of 

 andesite, somewhat altered, but still fresh enough to show 

 the twinning of the porphyritic feldspars. 



A section of the calcareous rock shows that it is appar- 

 ently free from the angular fragments of the shaly speci- 

 mens, while, as before, the mass of the rock appears to 

 consist of organic remains. With crossed nicols the larger 

 molds are seen to be filled with calcite. The ground-mass 

 of the rock is not isotropic, but gives the delicate polariza- 

 tion tints of calcite. With a high power the entire rock is 

 seen to have a microcrystalline structure, being made up of 

 irregular grains of calcite. This structure bears no rela- 

 tion to the distribution of the organic material in the rock, 

 except in the case of the Foraminifera. 



Character of the Organic Remains. A number of small 

 fragments of the shale were forwarded by Prof. Lawson to 

 Dr. George J. Hinde for examination. He has kindly 

 placed his conclusions at Prof. Lawson's disposal, in the 

 following note. 



"From small samples of these rocks sent over to me by 

 Prof. A. C. Lawson I have prepared thin microscopic sec- 

 tions where the material was sufficiently coherent to allow 

 of such being made, and in the case of the very soft rocks 

 the fine powder has been mounted just as it occurs, without 

 washing away the finer debris. I have only aimed in the 

 following notes at giving a general idea of the nature of the 

 organisms of which the rocks are composed, for the task of 

 recognizing even the genera present would prove too long 



