The Lingam Purana states: The foremost Lingam which is devoid of colour, taste, hearing, touch etc is spoken of as Prakriti or nature. The nature itself is a Lingam (or symbol) of Shiva.

The Lingam Purana states:
प्रधानं प्रकृतिर यदाहुर्लिगंउत्त म ।
गंध-वर्ण-रसहिंन ं शब्द-स्पर्शादिव र्जितं ॥
Meaning:
The foremost Lingam which is
devoid of colour, taste, hearing,
touch etc is spoken of as Prakriti or nature.
The nature itself is a Lingam (or symbol) of Shiva. When we see
nature, we infer the presence of its
creator – Shiva. Shiva Lingam is the
mark of Shiva the creator, Shiva the
sustainer and Shiva the destructor.
It also dispels another myth in
which Shiva is considered only as a
destructor.
Another authentic reference comes
from Skanda Purana where lingam
is clearly indicated as the supreme
Shiva from where the whole
universe is created and where it
finally submerge.

आकाशं लिंगमित्याहु: पृथ्वी तस्य पीठिका।
आलय: सर्व देवानां लयनार्लिंगमुच्य ते ॥
(स्कन्द पुराण)
The endless sky (that great void
which contains the entire
universe) is the Linga, the Earth is
its base. At the end of time the
entire universe and all the Gods
finally emerge in the Linga itself.