1889.] NEW YOKK ACADEMY OF SCIENCES. 35 



also contains a specimen of Mytihisedidis. The magma coukl 

 easily be removed, and after exposure to the air it became dry ar.d 

 firm. The northern outspur of this range happened to be a 

 peculiar rock formation of considerable thickness. This dark- 

 colored rock is strongly ferruginous ; it is the youngest member 

 of the Lake Merced region, which is considered to be of Tertiary- 

 origin. After heating a small piece in muriatic acid, a gritty 

 pulp remained, which to the touch felt like infusorial earth. The 

 microscopical examination gave a very interesting result. The 

 first look at the slide showed a striking likeness with the view 

 given by a drop of water taken from the sediment of an aquarium 

 or a collection of marsh-water material. How was I prepared to 

 recognize this fact immediately ? I have been studying protozoan 

 life for years, and in order to become especially acquainted with the 

 rock-building material furnished by protozoa, I collected speci- 

 mens from all different sources; and being familiar with the na- 

 tural habitat of the different protozoan divisions, — some feeding 

 and living in the water, top or bottom, others being firmly attached 

 to plants, while others only breed and vegetate in the ooze and 

 sediment, — I had no difficulty in providing myself with abun- 

 dant and favorable material, I put the material in large, flat 

 dishes and left it undisturbed for months. Let us take one of the 

 dishes, in which life is absolutely extinct, and subject it to a care- 

 ful scrutiny with the naked eye. We observe an amorphous, soft, 

 pulverulent mass, of various shades of color, and, generally along 

 the periphery of the dish and slightly floating, a considerable 

 quantity of larger spherical masses, consisting of the excreta of 

 vermes (Serpula, Nais, Planaria, etc.), Crustacea (GammaruF, 

 Cypris, Cyclop?, etc.), and rotatoria (Rotifer and Hydatina). 

 But we have to resort to the microscope in order to differentiate 

 this amorphous mass. As the ultimate result we obtain : — 



1. A granular organic detritus, vegetable and excrementitious; 

 these two can often not be distinguished in the absence of chloro- 

 pbylL 



2. The mineral remains — siliceous or calcareous — shells, skele- 

 tons, cuirasses, envelopes, encasing?, etc. 



Some of these mineral remains preserve the typical character 

 of the living protozoan, the skeleton of which forms its most im- 

 portant characteristic; the color, ornamentation, etc., being an 

 essential guide to a diagnosis. Such are : — 



{a) Thecoflagellata — Trachelomonas and Phacus; andThecoci- 

 lioflagellata — Peridium. 



ih) Diatomea?. 



{c) Thalamophora or Foraminifera. 



{(l) Heliozoa. 



{e) Radiolaria. 



