THE RECORD FROM FOSSILS. 99 



as they are known to-day. Inasmuch as this will 

 necessarily lead to considerable detail which will be 

 uninteresting to the general reader, this part of our 

 subject may be omitted without any break in con- 

 tinuity. 



PROTOZOA. 



The unicellular animals are all minute, and most of them are 

 entirely soft. For these reasons they are not well adapted for 

 preservation as fossils, and only one of the three classes has been 

 preserved in the rocks to any 'great extent. 



The Foraminifera have usually a shell of lime, and therefore have 

 left traces of themselves in all ages. Even in the Archean (i) there 

 is a curious body (Eozoan Canadense) believed by some to be the 

 remains of Foraminifera, though it is usually regarded to-day as a 

 mineral deposit. With the Silurian (2), however, true foraminifers 

 appeared unquestionably in abundance, and every subsequent age 

 shows traces of their presence. There are two geological periods in 

 which their deposits are of special importance. The immense chalk 

 beds of Cretaceous (8) are made very largely of shells of foraminifers. 

 This chalk is almost exactly the same in its formation as the so-called 

 Globergerina ooze that is being deposited now at the bottom of the 

 ocean, so that it seems that chalk is still being formed in our modern 

 seas. The second large deposit of foraminifers is the Numulitic lime- 

 stone of the Tertiary, an immense bed of European rocks covering 

 thousands of miles of territory. We must not conclude that in 

 these two periods the Foraminifera were any more abundant than in 

 others, but simply that the conditions were more favorable for their 

 preservation. It is remarkably interesting that the species existing 

 in the Tertiary (9) and many of those of the Cretaceous (8) chalk are 

 identical with species found living to-day, and when we go still 

 further back in history the amount cf change is very slight. Indeed, 

 Dr. Carpenter says there is no evidence of any fundamental modifica- 

 tion or advance of the foraminiferous type from the Paleozoic period 

 to the present time. 



A second order of the Protozoa, the Radiolaria, possess a skeleton 

 of silica which is tolerably well adapted for preservation. These 

 have been traced back as far as the Silurian (2), though it is not until 



