The notes on tortoises written by Miguel Castro in 1965, a fragment of which is presented in the image accompanying this text, are but one of the many unpublished texts (original or copies) held at the CDF’s Library, within the so-called "Special Collections".

Some of those documents are original manuscripts or typographic texts. A second group is composed by typographic, edited copies of handwritten notes. Finally, there are copies (mimeographed, photocopied) of the previous items.

Most of them are unpublished documents: personal notes, travel diaries, or internal reports produced by / for the CDF, all of them concerning Galapagos or its biodiversity. They are comprised into the category known as "grey literature": materials and research produced by organizations outside of the traditional commercial or academic publishing and distribution channels.

The value of these documents is twofold. On the one hand, they contain primary, unpublished raw data that on many occasions have served as the basis for well-known academic literature (articles and books). On the other, they include a mixture of scientific and personal speech that makes part of a particular social, cultural, and historical context — which is important to understand the reasons behind the academic work, the personal opinions, the circumstances, failures and problems, etc.

Unpublished, original texts remain a very important source of primary information, first-hand descriptions, and original impressions.